/* ============================================================
   JGEC Study Portal — Design System
   Premium dark-mode study interface
   ============================================================ */

/* ── Accessibility & Skip Link ── */
:focus-visible {
  outline: 2px solid var(--accent-indigo);
  outline-offset: 2px;
}

.skip-link {
  position: absolute;
  top: -60px;
  left: 12px;
  background: var(--accent-indigo);
  color: #ffffff;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  z-index: 9999;
  font-weight: 600;
  font-size: 13px;
  transition: top var(--transition-fast);
  text-decoration: none;
  box-shadow: var(--shadow-md);
}

.skip-link:focus {
  top: 12px;
}

.reading-progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  width: 0%;
  background: var(--accent-gradient);
  z-index: 1001;
  transition: width 0.1s ease;
}

.top-bar-left {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: max-content;
  flex-shrink: 0;
}

/* ── CSS Custom Properties ── */
:root {
  /* Background layers */
  --bg-base: #09090b;
  --bg-sidebar: #0f0f14;
  --bg-card: #18181b;
  --bg-card-hover: #1e1e24;
  --bg-elevated: #27272a;
  --bg-input: #1a1a22;

  /* Borders */
  --border-subtle: #27272a;
  --border-default: #3f3f46;
  --border-strong: #52525b;

  /* Text — WCAG AA High Contrast Compliant */
  --text-primary: #fafafa;
  --text-secondary: #d4d4d8;
  --text-muted: #a1a1aa;
  --text-dimmed: #787885;

  /* Accent */
  --accent-indigo: #818cf8;
  --accent-violet: #a78bfa;
  --accent-blue: #60a5fa;
  --accent-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --accent-gradient-text: linear-gradient(135deg, #818cf8 0%, #c084fc 100%);
  --accent-glow: rgba(129, 140, 248, 0.15);

  /* Semantic */
  --success: #4ade80;
  --success-bg: rgba(74, 222, 128, 0.08);
  --success-border: rgba(74, 222, 128, 0.2);
  --warning: #fbbf24;
  --warning-bg: rgba(251, 191, 36, 0.08);
  --warning-border: rgba(251, 191, 36, 0.2);
  --error: #f87171;
  --error-bg: rgba(248, 113, 113, 0.08);
  --error-border: rgba(248, 113, 113, 0.2);
  --info: #60a5fa;
  --info-bg: rgba(96, 165, 250, 0.08);
  --info-border: rgba(96, 165, 250, 0.2);

  /* Layout */
  --sidebar-width: 300px;
  --header-height: 60px;
  --content-max-width: 860px;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 20px;

  /* Transitions */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.5);
  --shadow-glow: 0 0 20px rgba(129, 140, 248, 0.15);
}

/* ── Reset & Base ── */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-base);
  color: var(--text-primary);
  line-height: 1.7;
  overflow: hidden;
  height: 100vh;
}

/* ── Custom Scrollbar ── */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}
::-webkit-scrollbar-track {
  background: transparent;
}
::-webkit-scrollbar-thumb {
  background: var(--border-default);
  border-radius: 10px;
}
::-webkit-scrollbar-thumb:hover {
  background: var(--border-strong);
}

/* ── Layout Shell ── */
.app-layout {
  display: flex;
  height: 100vh;
  width: 100vw;
}

/* ── Sidebar ── */
.sidebar {
  width: var(--sidebar-width);
  min-width: var(--sidebar-width);
  height: 100vh;
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border-subtle);
  display: flex;
  flex-direction: column;
  transition: transform var(--transition-base);
  z-index: 100;
  overflow: hidden;
}

.sidebar-header {
  padding: 20px 20px 16px;
  border-bottom: 1px solid var(--border-subtle);
  flex-shrink: 0;
}

.sidebar-logo {
  display: flex;
  align-items: center;
  gap: 12px;
}

.sidebar-logo-icon {
  width: 38px;
  height: 38px;
  background: var(--accent-gradient);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  font-weight: 700;
  color: white;
  box-shadow: var(--shadow-glow);
}

.sidebar-logo-text {
  display: flex;
  flex-direction: column;
}

.sidebar-logo-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.3px;
}

.sidebar-logo-subtitle {
  font-size: 11px;
  color: var(--text-muted);
  font-weight: 500;
  letter-spacing: 0.5px;
  text-transform: uppercase;
}

.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: 12px 10px;
}

/* Subject Item in Sidebar */
.subject-item {
  margin-bottom: 2px;
}

.subject-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 12px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  user-select: none;
  position: relative;
}

.subject-header:hover {
  background: var(--bg-card);
}

.subject-header.active {
  background: var(--accent-glow);
}

.subject-icon {
  width: 30px;
  height: 30px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 15px;
  flex-shrink: 0;
  background: var(--bg-elevated);
  transition: all var(--transition-fast);
}

.subject-header:hover .subject-icon {
  transform: scale(1.05);
}

.subject-info {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.subject-name {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  line-height: 1.3;
}

.subject-code {
  font-size: 10px;
  font-weight: 500;
  color: var(--text-muted);
  font-family: 'JetBrains Mono', monospace;
}

.subject-progress-mini {
  width: 100%;
  height: 2px;
  background: var(--border-subtle);
  border-radius: 10px;
  overflow: hidden;
  margin-top: 2px;
}

.subject-progress-mini-fill {
  height: 100%;
  background: var(--accent-gradient);
  border-radius: 10px;
  transition: width var(--transition-slow);
}

.subject-chevron {
  font-size: 12px;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
  flex-shrink: 0;
}

.subject-header.expanded .subject-chevron {
  transform: rotate(90deg);
}

/* Module List (collapsible) */
.module-list {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
  padding-left: 22px;
}

.module-list.open {
  max-height: 2000px;
}

.module-group {
  margin-bottom: 4px;
}

.module-group-label {
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--text-dimmed);
  padding: 10px 12px 4px;
}

.chapter-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 12px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 12.5px;
  color: var(--text-secondary);
  border-left: 2px solid transparent;
  margin-left: 8px;
}

.chapter-item:hover {
  color: var(--text-primary);
  background: var(--bg-card);
  border-left-color: var(--border-default);
}

.chapter-item.active {
  color: var(--accent-indigo);
  background: var(--accent-glow);
  border-left-color: var(--accent-indigo);
  font-weight: 500;
}

.chapter-item.coming-soon {
  opacity: 0.4;
  pointer-events: none;
}

.chapter-status {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  flex-shrink: 0;
}

.chapter-status.not-started {
  border: 1.5px solid var(--text-dimmed);
  background: transparent;
}

.chapter-status.in-progress {
  background: var(--warning);
  box-shadow: 0 0 6px rgba(251, 191, 36, 0.4);
}

.chapter-status.completed {
  background: var(--success);
  box-shadow: 0 0 6px rgba(74, 222, 128, 0.4);
}

.chapter-name {
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ── Main Content Area ── */
.main-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

/* Top Header Bar */
.top-bar {
  height: var(--header-height);
  min-height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 28px;
  gap: 16px;
  border-bottom: 1px solid var(--border-subtle);
  background: rgba(9, 9, 11, 0.8);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  z-index: 50;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
}

.breadcrumb-item {
  color: var(--text-muted);
  cursor: pointer;
  transition: color var(--transition-fast);
}

.breadcrumb-item:hover {
  color: var(--text-primary);
}

.breadcrumb-sep {
  color: var(--text-dimmed);
  font-size: 10px;
}

.breadcrumb-current {
  color: var(--text-primary);
  font-weight: 500;
}

.top-bar-actions {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
}

.btn-icon {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  background: var(--bg-card);
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 16px;
}

.btn-icon:hover {
  background: var(--bg-elevated);
  color: var(--text-primary);
  border-color: var(--border-default);
}

.mobile-menu-btn {
  display: none;
}

/* Content Scroll Area */
.content-scroll {
  flex: 1;
  overflow-y: auto;
  padding: 40px 48px 80px;
  scroll-padding-top: 85px;
  scroll-padding-bottom: 115px;
}

.content-wrapper {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

/* ── Home / Dashboard View ── */
.home-view {
  animation: fadeInUp 0.4s ease;
}

.home-hero {
  text-align: center;
  margin-bottom: 48px;
  padding: 48px 0 32px;
}

.home-hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 14px;
  background: var(--accent-glow);
  border: 1px solid rgba(129, 140, 248, 0.2);
  border-radius: 100px;
  font-size: 12px;
  font-weight: 500;
  color: var(--accent-indigo);
  margin-bottom: 20px;
}

.home-hero h1 {
  font-size: 40px;
  font-weight: 800;
  letter-spacing: -1.5px;
  line-height: 1.1;
  margin-bottom: 14px;
  background: var(--accent-gradient-text);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.home-hero p {
  font-size: 16px;
  color: var(--text-secondary);
  max-width: 520px;
  margin: 0 auto;
  line-height: 1.6;
}

.home-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-bottom: 40px;
}

.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 22px;
  text-align: center;
  transition: all var(--transition-base);
}

.stat-card:hover {
  border-color: var(--border-default);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.stat-value {
  font-size: 32px;
  font-weight: 700;
  background: var(--accent-gradient-text);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.stat-label {
  font-size: 12px;
  color: var(--text-muted);
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-top: 4px;
}

.home-section-title {
  font-size: 18px;
  font-weight: 700;
  margin-bottom: 18px;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 14px;
}

.subject-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

.subject-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--card-accent, var(--accent-gradient));
  opacity: 0;
  transition: opacity var(--transition-base);
}

.subject-card:hover {
  border-color: var(--border-default);
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}

.subject-card:hover::before {
  opacity: 1;
}

.subject-card-header {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  margin-bottom: 14px;
}

.subject-card-icon {
  width: 42px;
  height: 42px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  flex-shrink: 0;
  background: var(--bg-elevated);
}

.subject-card-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-primary);
  line-height: 1.35;
}

.subject-card-code {
  font-size: 11px;
  font-family: 'JetBrains Mono', monospace;
  color: var(--text-muted);
  margin-top: 2px;
}

.subject-card-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 11px;
  color: var(--text-muted);
  margin-bottom: 14px;
}

.subject-card-meta span {
  display: flex;
  align-items: center;
  gap: 4px;
}

.subject-card-progress {
  width: 100%;
  height: 4px;
  background: var(--border-subtle);
  border-radius: 10px;
  overflow: hidden;
}

.subject-card-progress-fill {
  height: 100%;
  background: var(--accent-gradient);
  border-radius: 10px;
  transition: width var(--transition-slow);
}

.subject-card-badge {
  display: inline-flex;
  align-items: center;
  padding: 3px 8px;
  border-radius: 100px;
  font-size: 10px;
  font-weight: 600;
  background: var(--info-bg);
  color: var(--info);
  border: 1px solid var(--info-border);
}

.subject-card-badge.coming {
  background: var(--bg-elevated);
  color: var(--text-muted);
  border-color: var(--border-default);
}

/* ── Content / Chapter View ── */
.chapter-view {
  animation: fadeIn 0.15s ease-out;
  contain: layout style;
}

.chapter-header {
  margin-bottom: 40px;
  padding-bottom: 28px;
  border-bottom: 1px solid var(--border-subtle);
}

.chapter-header-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  background: var(--accent-glow);
  border: 1px solid rgba(129, 140, 248, 0.2);
  border-radius: 100px;
  font-size: 11px;
  font-weight: 600;
  color: var(--accent-indigo);
  margin-bottom: 14px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.chapter-header h1 {
  font-size: 32px;
  font-weight: 800;
  letter-spacing: -0.8px;
  line-height: 1.15;
  margin-bottom: 10px;
  color: var(--text-primary);
}

.chapter-header p {
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* ── Content Typography ── */
.content-body h2 {
  font-size: 24px;
  font-weight: 700;
  color: var(--text-primary);
  margin: 48px 0 16px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border-subtle);
  letter-spacing: -0.3px;
}

.content-body h2:first-child {
  margin-top: 0;
}

.content-body h3 {
  font-size: 18px;
  font-weight: 600;
  color: var(--text-primary);
  margin: 32px 0 12px;
}

.content-body h4 {
  font-size: 15px;
  font-weight: 600;
  color: var(--accent-indigo);
  margin: 24px 0 10px;
}

.content-body p {
  margin-bottom: 16px;
  color: var(--text-secondary);
  font-size: 15px;
  line-height: 1.8;
}

.content-body strong {
  color: var(--text-primary);
  font-weight: 600;
}

.content-body ul, .content-body ol {
  margin-bottom: 16px;
  padding-left: 24px;
}

.content-body li {
  margin-bottom: 6px;
  color: var(--text-secondary);
  font-size: 15px;
  line-height: 1.7;
}

.content-body li strong {
  color: var(--text-primary);
}

/* ── Formula / Math Display ── */
.content-body .katex-display {
  margin: 20px 0;
  padding: 16px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  overflow-x: auto;
}

.content-body .katex {
  font-size: 1.08em;
}

/* ── Tables ── */
.content-body table {
  width: 100%;
  border-collapse: collapse;
  margin: 20px 0;
  font-size: 14px;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}

.content-body thead {
  background: var(--bg-elevated);
}

.content-body th {
  padding: 12px 16px;
  text-align: left;
  font-weight: 600;
  color: var(--text-primary);
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  border-bottom: 1px solid var(--border-default);
}

.content-body td {
  padding: 10px 16px;
  border-bottom: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  line-height: 1.6;
}

.content-body tbody tr:hover {
  background: var(--bg-card-hover);
}

.content-body tbody tr:last-child td {
  border-bottom: none;
}

/* ── Content Boxes (Concept, Warning, Tip, Example, PYQ) ── */
.content-box {
  border-radius: var(--radius-md);
  padding: 18px 22px;
  margin: 22px 0;
  border-left: 4px solid;
  position: relative;
}

.content-box-title {
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.6px;
  margin-bottom: 10px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.box-concept {
  background: var(--info-bg);
  border-color: var(--info);
}
.box-concept .content-box-title { color: var(--info); }

.box-teacher {
  background: rgba(167, 139, 250, 0.08);
  border-color: var(--accent-violet);
}
.box-teacher .content-box-title { color: var(--accent-violet); }

.box-warning {
  background: var(--warning-bg);
  border-color: var(--warning);
}
.box-warning .content-box-title { color: var(--warning); }

.box-tip {
  background: var(--success-bg);
  border-color: var(--success);
}
.box-tip .content-box-title { color: var(--success); }

.box-example {
  background: var(--bg-card);
  border-color: var(--accent-indigo);
  border: 1px solid var(--border-subtle);
  border-left: 4px solid var(--accent-indigo);
}
.box-example .content-box-title { color: var(--accent-indigo); }

.box-pyq {
  background: rgba(248, 113, 113, 0.06);
  border-color: var(--error);
}
.box-pyq .content-box-title { color: var(--error); }

.box-practice {
  background: rgba(251, 191, 36, 0.06);
  border-color: var(--warning);
}
.box-practice .content-box-title { color: var(--warning); }

/* Step-by-step Solutions */
.step {
  display: flex;
  gap: 14px;
  margin: 12px 0;
  padding: 10px 0;
}

.step-num {
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: var(--accent-gradient);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 700;
  color: white;
  flex-shrink: 0;
  margin-top: 2px;
}

.step-content {
  flex: 1;
}

.step-content p {
  margin-bottom: 8px;
}

/* ── Progress Checkbox in Chapter View ── */
.chapter-progress-toggle {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 13px;
  color: var(--text-secondary);
  margin-top: 20px;
  user-select: none;
}

.chapter-progress-toggle:hover {
  border-color: var(--border-default);
  background: var(--bg-card-hover);
}

.chapter-progress-toggle.completed {
  border-color: var(--success-border);
  background: var(--success-bg);
  color: var(--success);
}

.chapter-progress-toggle .check-icon {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  border: 2px solid var(--border-default);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.chapter-progress-toggle.completed .check-icon {
  background: var(--success);
  border-color: var(--success);
  color: var(--bg-base);
  font-size: 12px;
}

/* ── Bottom Navigation ── */
.bottom-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 56px;
  padding-top: 28px;
  border-top: 1px solid var(--border-subtle);
  gap: 16px;
}

.bottom-nav-btn {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 22px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
  max-width: 48%;
}

.bottom-nav-btn:hover {
  border-color: var(--border-default);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.bottom-nav-btn .label {
  font-size: 11px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.bottom-nav-btn .title {
  font-size: 14px;
  font-weight: 500;
  color: var(--text-primary);
}

.bottom-nav-btn .arrow {
  font-size: 18px;
  color: var(--text-muted);
}

.bottom-nav-btn.next {
  margin-left: auto;
  text-align: right;
}

/* ── Animations ── */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

/* ── Mobile Responsive ── */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.6);
  z-index: 90;
  opacity: 0;
  transition: opacity var(--transition-base);
}

.sidebar-overlay.visible {
  display: block;
  opacity: 1;
}

@media (max-width: 768px) {
  .sidebar {
    position: fixed;
    left: 0;
    top: 0;
    transform: translateX(-100%);
    box-shadow: var(--shadow-lg);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .mobile-menu-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 44px;
    min-height: 44px;
    width: 44px;
    height: 44px;
    padding: 0;
    border-radius: 10px;
    font-size: 22px;
    line-height: 1;
    background: var(--bg-elevated);
    border: 1.5px solid rgba(129, 140, 248, 0.4);
    color: var(--text-primary);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.25);
    cursor: pointer;
    flex-shrink: 0;
    transition: all var(--transition-fast);
  }
  .mobile-menu-btn:hover,
  .mobile-menu-btn:active {
    background: rgba(129, 140, 248, 0.18);
    border-color: var(--accent-indigo);
    color: #ffffff;
    transform: scale(1.04);
  }

  .top-bar {
    padding: 0 12px;
    gap: 8px;
  }

  .top-bar-left {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-shrink: 0;
    min-width: max-content;
  }

  .breadcrumb {
    display: none;
  }

  .search-trigger {
    min-width: 0 !important;
    width: auto !important;
    flex: 1 1 auto;
    padding: 6px 10px;
    gap: 6px;
    overflow: hidden;
  }

  .search-trigger .search-shortcut {
    display: none;
  }

  .search-trigger .search-placeholder {
    display: inline-block !important;
    font-size: 12px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }

  .search-text-full {
    display: none !important;
  }

  .search-text-short {
    display: inline !important;
  }

  .top-bar-actions {
    display: flex;
    align-items: center;
    gap: 6px;
    flex-shrink: 0;
  }

  .btn-topbar {
    padding: 0 8px;
    min-width: 36px;
    height: 36px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }

  .btn-topbar-text {
    display: none;
  }

  .content-scroll {
    padding: 24px 16px 60px;
  }

  .home-hero h1 {
    font-size: 28px;
  }

  .home-stats {
    grid-template-columns: 1fr;
  }

  .subject-grid {
    grid-template-columns: 1fr;
  }

  .chapter-header h1 {
    font-size: 22px;
  }

  .bottom-nav {
    flex-direction: column;
  }

  .bottom-nav-btn {
    max-width: 100%;
    width: 100%;
  }

  .formula-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .top-bar {
    padding: 0 8px;
    gap: 6px;
  }

  .top-bar-left {
    display: flex;
    align-items: center;
    gap: 6px;
    flex-shrink: 0;
    min-width: max-content;
  }

  .mobile-menu-btn {
    min-width: 40px;
    min-height: 40px;
    width: 40px;
    height: 40px;
    font-size: 18px;
  }

  .btn-topbar-back {
    padding: 6px 8px;
    font-size: 12px;
    min-width: 32px;
    height: 34px;
  }

  .btn-topbar-back .btn-back-text {
    display: none;
  }

  .search-trigger {
    min-width: 0 !important;
    flex: 1 1 auto;
    padding: 6px 8px;
    gap: 5px;
    border-radius: var(--radius-sm);
  }

  .search-trigger::after {
    display: none !important;
  }

  .search-trigger .search-placeholder {
    font-size: 11px;
    max-width: 100px;
    display: inline-block !important;
  }

  .top-bar-actions {
    gap: 4px;
    flex-shrink: 0;
  }

  .btn-topbar,
  .top-bar-actions .btn-icon {
    width: 34px;
    min-width: 34px;
    height: 34px;
    font-size: 14px;
    padding: 0;
  }

  .content-scroll {
    padding: 16px 12px 60px;
  }

  .content-body h2 {
    font-size: 19px;
  }

  .content-box {
    padding: 12px 14px;
  }

  .stat-card {
    padding: 16px;
  }

  .subject-hero {
    padding: 20px 16px;
  }

  .subject-hero-title {
    font-size: 20px;
  }

  .module-syllabus-card {
    padding: 16px;
  }

  .module-chapters-list {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 360px) {
  .top-bar {
    padding: 0 6px;
    gap: 4px;
  }

  .top-bar-left {
    gap: 4px;
  }

  .mobile-menu-btn {
    min-width: 38px;
    width: 38px;
    height: 38px;
    font-size: 17px;
  }

  .btn-topbar-back {
    min-width: 30px;
    height: 32px;
    padding: 4px 6px;
    font-size: 11px;
  }

  .search-trigger .search-placeholder {
    display: none !important;
  }

  .search-trigger {
    flex: 0 0 auto;
    width: 34px;
    min-width: 34px !important;
    height: 34px;
    padding: 0;
    justify-content: center;
  }

  .top-bar-actions {
    gap: 3px;
  }

  .btn-topbar,
  .top-bar-actions .btn-icon {
    width: 32px;
    min-width: 32px;
    height: 32px;
    font-size: 13px;
  }
}



/* ── Collapsible Sections ── */
.collapsible {
  margin: 16px 0;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.collapsible-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 18px;
  background: var(--bg-card);
  cursor: pointer;
  user-select: none;
  transition: background var(--transition-fast);
  font-size: 14px;
  font-weight: 600;
  color: var(--text-primary);
}

.collapsible-header:hover {
  background: var(--bg-card-hover);
}

.collapsible-chevron {
  font-size: 12px;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
}

.collapsible.open .collapsible-chevron {
  transform: rotate(90deg);
}

.collapsible-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
  padding: 0 18px;
}

.collapsible.open .collapsible-body {
  max-height: 5000px;
  padding: 14px 18px 18px;
}

/* ── Code blocks ── */
.content-body code {
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  background: var(--bg-elevated);
  padding: 2px 7px;
  border-radius: 4px;
  color: var(--accent-indigo);
  border: 1px solid var(--border-subtle);
}

.content-body pre {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 18px;
  overflow-x: auto;
  margin: 16px 0;
}

.content-body pre code {
  background: none;
  border: none;
  padding: 0;
  color: var(--text-secondary);
}

/* ── Highlight / Result Box ── */
.result-box {
  background: var(--accent-glow);
  border: 1px solid rgba(129, 140, 248, 0.25);
  border-radius: var(--radius-md);
  padding: 16px 20px;
  margin: 16px 0;
  text-align: center;
}

.result-box p {
  color: var(--accent-indigo);
  font-weight: 600;
  margin: 0;
}

/* ── Divider ── */
.content-body hr {
  border: none;
  height: 1px;
  background: var(--border-subtle);
  margin: 32px 0;
}

/* ── Top Bar Search & Actions ── */
.search-trigger {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 7px 14px;
  cursor: pointer;
  transition: all var(--transition-fast);
  color: var(--text-muted);
  font-size: 13px;
  min-width: 0;
}

@media (min-width: 769px) {
  .search-trigger {
    min-width: 260px;
  }
}

.search-trigger:hover {
  background: var(--bg-elevated);
  border-color: var(--border-default);
  color: var(--text-secondary);
  box-shadow: 0 0 12px rgba(129, 140, 248, 0.15);
}

.search-trigger .search-icon {
  font-size: 13px;
  opacity: 0.8;
}

.search-trigger .search-placeholder {
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.search-text-short {
  display: none;
}

.search-text-full {
  display: inline;
}

.search-shortcut {
  font-size: 11px;
  padding: 2px 6px;
  border-radius: 4px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  font-family: 'JetBrains Mono', monospace;
}

.btn-topbar {
  display: flex;
  align-items: center;
  gap: 6px;
  height: 36px;
  padding: 0 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  background: var(--bg-card);
  color: var(--text-secondary);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
}

.btn-topbar:hover {
  background: var(--bg-elevated);
  color: var(--text-primary);
  border-color: var(--border-default);
}

/* ── Global Search Modal ── */
.search-modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.75);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 1000;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 10vh;
}

.search-modal-backdrop.open {
  display: flex;
}

.search-modal-box {
  background: #121217;
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  width: 90%;
  max-width: 640px;
  max-height: 80vh;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.7), 0 0 30px rgba(129, 140, 248, 0.15);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: modalSlideDown 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

@keyframes modalSlideDown {
  from { opacity: 0; transform: translateY(-16px) scale(0.98); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

.search-input-wrapper {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border-subtle);
  background: var(--bg-card);
}

.search-input-icon {
  font-size: 18px;
  opacity: 0.7;
}

.search-input-wrapper input {
  flex: 1;
  background: transparent;
  border: none;
  outline: none;
  color: var(--text-primary);
  font-size: 16px;
  font-family: inherit;
}

.search-input-wrapper input::placeholder {
  color: var(--text-muted);
}

.search-close-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 16px;
  padding: 4px;
  border-radius: 4px;
  transition: color var(--transition-fast);
}

.search-close-btn:hover {
  color: var(--text-primary);
}

.search-filters {
  display: flex;
  gap: 8px;
  padding: 10px 20px;
  border-bottom: 1px solid var(--border-subtle);
  background: rgba(15, 15, 20, 0.6);
  overflow-x: auto;
}

.filter-chip {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  font-size: 12px;
  padding: 4px 12px;
  border-radius: 20px;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.filter-chip:hover {
  border-color: var(--border-default);
  color: var(--text-primary);
}

.filter-chip.active {
  background: var(--accent-indigo);
  border-color: var(--accent-indigo);
  color: #fff;
  font-weight: 500;
}

.search-results-list {
  flex: 1;
  overflow-y: auto;
  padding: 8px 12px;
  max-height: 50vh;
}

.search-result-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  border: 1px solid transparent;
  margin-bottom: 4px;
}

.search-result-item:hover, .search-result-item.selected {
  background: var(--bg-card);
  border-color: var(--border-subtle);
}

.search-result-item.selected {
  border-color: var(--accent-indigo);
  background: rgba(129, 140, 248, 0.08);
}

.search-result-icon {
  font-size: 16px;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-elevated);
  border-radius: var(--radius-sm);
  flex-shrink: 0;
}

.search-result-content {
  flex: 1;
  min-width: 0;
}

.search-result-title {
  font-size: 13.5px;
  font-weight: 500;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.search-result-title mark {
  background: rgba(129, 140, 248, 0.35);
  color: #fff;
  padding: 1px 3px;
  border-radius: 2px;
}

.search-result-meta {
  font-size: 11px;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 2px;
}

.search-result-badge {
  font-size: 10px;
  font-weight: 600;
  padding: 2px 6px;
  border-radius: 4px;
  background: var(--bg-elevated);
  color: var(--accent-indigo);
  font-family: 'JetBrains Mono', monospace;
}

.search-tier-badge {
  font-size: 9.5px;
  font-weight: 700;
  padding: 1.5px 6px;
  border-radius: 4px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.search-tier-badge.theory {
  background: rgba(129, 140, 248, 0.15);
  color: #a5b4fc;
  border: 1px solid rgba(129, 140, 248, 0.3);
}
.search-tier-badge.lab {
  background: rgba(56, 189, 248, 0.15);
  color: #38bdf8;
  border: 1px solid rgba(56, 189, 248, 0.35);
}

.search-modal-footer {
  padding: 10px 20px;
  border-top: 1px solid var(--border-subtle);
  background: var(--bg-card);
  display: flex;
  gap: 16px;
  font-size: 11px;
  color: var(--text-muted);
}

.search-modal-footer kbd {
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  padding: 1px 5px;
  border-radius: 3px;
  font-family: 'JetBrains Mono', monospace;
}

.search-empty {
  padding: 40px 20px;
  text-align: center;
  color: var(--text-muted);
  font-size: 13.5px;
}

/* ── Chapter Header Actions (Listen & Print Buttons) ── */
.chapter-header-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.btn-print,
.tts-chapter-header-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  height: 36px;
  padding: 0 14px;
  border-radius: var(--radius-sm);
  font-size: 12.5px;
  font-weight: 600;
  cursor: pointer;
  margin: 0;
  line-height: 1;
  box-sizing: border-box;
  vertical-align: middle;
  transition: all var(--transition-fast);
}

.btn-print {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
}

.btn-print:hover {
  background: var(--bg-elevated);
  color: var(--text-primary);
  border-color: var(--accent-indigo);
  box-shadow: 0 0 10px rgba(129, 140, 248, 0.15);
}

/* ── Subject Syllabus Dashboard ── */
.subject-dashboard {
  animation: fadeInUp 0.35s ease;
}

.subject-hero {
  background: linear-gradient(135deg, rgba(30, 30, 42, 0.8) 0%, rgba(15, 15, 22, 0.95) 100%);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 28px;
  margin-bottom: 32px;
  position: relative;
  overflow: hidden;
}

.subject-hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--subject-accent, var(--accent-indigo));
}

.subject-hero-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 20px;
  flex-wrap: wrap;
}

.subject-hero-left {
  display: flex;
  gap: 16px;
  align-items: center;
}

.subject-hero-icon {
  width: 54px;
  height: 54px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 26px;
  color: var(--subject-accent, var(--accent-indigo));
  box-shadow: 0 0 20px rgba(129, 140, 248, 0.15);
}

.subject-hero-code {
  font-size: 11px;
  font-weight: 600;
  color: var(--text-muted);
  font-family: 'JetBrains Mono', monospace;
  letter-spacing: 0.5px;
}

.subject-hero-title {
  font-size: 24px;
  font-weight: 700;
  color: var(--text-primary);
  margin-top: 2px;
  letter-spacing: -0.3px;
}

.subject-hero-pills {
  display: flex;
  gap: 8px;
  margin-top: 8px;
  flex-wrap: wrap;
}

.subject-pill {
  font-size: 11px;
  padding: 3px 8px;
  border-radius: 4px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
}

.subject-hero-actions {
  display: flex;
  gap: 10px;
  align-items: center;
}

.btn-primary-action {
  background: var(--accent-gradient);
  border: none;
  color: white;
  font-weight: 600;
  font-size: 13.5px;
  padding: 9px 18px;
  border-radius: var(--radius-md);
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 8px;
  transition: all var(--transition-fast);
  box-shadow: 0 4px 14px rgba(102, 126, 234, 0.35);
}

.btn-primary-action:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(102, 126, 234, 0.5);
}

.subject-progress-section {
  margin-top: 24px;
  padding-top: 18px;
  border-top: 1px solid var(--border-subtle);
}

.subject-progress-label {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.subject-progress-bar {
  width: 100%;
  height: 8px;
  background: var(--bg-card);
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}

.subject-progress-bar-fill {
  height: 100%;
  background: var(--accent-gradient);
  border-radius: 10px;
  transition: width var(--transition-slow);
}

/* Modules Grid in Dashboard */
.modules-syllabus-grid {
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.module-syllabus-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px 22px;
  transition: all var(--transition-fast);
}

.module-syllabus-card:hover {
  border-color: var(--border-default);
}

.module-syllabus-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border-subtle);
}

.module-syllabus-title-wrap {
  display: flex;
  align-items: center;
  gap: 10px;
}

.module-syllabus-icon {
  font-size: 18px;
}

.module-syllabus-title {
  font-size: 15px;
  font-weight: 600;
  color: var(--text-primary);
}

.module-syllabus-badge {
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 12px;
  background: var(--bg-elevated);
  color: var(--text-secondary);
}

.module-chapters-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 10px;
}

.module-chapter-card {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 14px;
  background: var(--bg-base);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.module-chapter-card:hover {
  background: var(--bg-elevated);
  border-color: var(--border-default);
  transform: translateY(-1px);
}

.module-chapter-card.completed {
  border-left: 3px solid var(--success);
}

.module-chapter-card.in-progress {
  border-left: 3px solid var(--warning);
}

.module-chapter-info {
  flex: 1;
  min-width: 0;
}

.module-chapter-name {
  font-size: 12.5px;
  font-weight: 500;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.module-chapter-sub {
  font-size: 10.5px;
  color: var(--text-muted);
  margin-top: 1px;
}

/* ── Formula Hub Modal ── */
.formula-modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.75);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 1000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.formula-modal-backdrop.open {
  display: flex;
}

.formula-modal-box {
  background: #121217;
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  width: 95%;
  max-width: 860px;
  max-height: 85vh;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.8), 0 0 30px rgba(129, 140, 248, 0.15);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: modalSlideDown 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.formula-modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border-subtle);
  background: var(--bg-card);
}

.formula-modal-header h2 {
  font-size: 16px;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
  min-width: 0;
  flex: 1;
  margin: 0;
  line-height: 1.35;
  word-break: break-word;
}

.formula-subject-tabs {
  display: flex;
  gap: 8px;
  padding: 10px 18px;
  border-bottom: 1px solid var(--border-subtle);
  background: rgba(15, 15, 20, 0.6);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: thin;
}

.formula-tab-btn {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  font-size: 12px;
  padding: 7px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  white-space: nowrap;
  flex-shrink: 0;
  min-height: 36px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.formula-tab-btn:hover {
  border-color: var(--border-default);
  color: var(--text-primary);
}

.formula-tab-btn.active {
  background: var(--accent-indigo);
  border-color: var(--accent-indigo);
  color: white;
  font-weight: 600;
}

.formula-content-scroll {
  flex: 1;
  overflow-y: auto;
  padding: 20px;
  scroll-padding-top: 20px;
  scroll-padding-bottom: 20px;
}

.formula-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 280px), 1fr));
  gap: 16px;
  width: 100%;
}

.formula-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 16px 18px;
  min-width: 0;
  max-width: 100%;
  box-sizing: border-box;
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.formula-card:hover {
  border-color: rgba(129, 140, 248, 0.3);
}

.formula-card-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--accent-indigo);
  margin-bottom: 10px;
  display: block;
  line-height: 1.4;
  word-break: break-word;
  overflow-wrap: break-word;
}

.formula-card-body {
  font-size: 13px;
  color: var(--text-primary);
  line-height: 1.65;
  overflow-x: auto;
  max-width: 100%;
  word-break: break-word;
  overflow-wrap: anywhere;
}

.formula-card-body .katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  max-width: 100%;
  padding: 6px 2px;
  margin: 8px 0;
  scrollbar-width: thin;
}

.formula-card-body table {
  width: 100%;
  font-size: 12px;
  border-collapse: collapse;
  margin: 10px 0;
  display: table;
  max-width: 100%;
  overflow-x: auto;
}

.formula-card-body th, .formula-card-body td {
  padding: 8px 10px;
  border: 1px solid var(--border-subtle);
  text-align: left;
}

.formula-card-body th {
  background: var(--bg-elevated);
  color: var(--accent-indigo);
  font-weight: 600;
}

/* ── Print / Save PDF Mode ── */
@media print {
  body {
    background: #ffffff !important;
    color: #111827 !important;
    overflow: visible !important;
    height: auto !important;
    font-size: 11pt;
    line-height: 1.5;
  }
  .sidebar, 
  .top-bar, 
  .bottom-nav, 
  .chapter-progress-toggle, 
  .btn-print, 
  .search-modal-backdrop, 
  .formula-modal-backdrop,
  .sidebar-overlay,
  .btn-icon {
    display: none !important;
  }
  .app-layout {
    display: block !important;
    height: auto !important;
    width: 100% !important;
  }
  .main-area {
    display: block !important;
    overflow: visible !important;
    height: auto !important;
  }
  .content-scroll {
    overflow: visible !important;
    height: auto !important;
    padding: 0 !important;
  }
  .content-wrapper, .chapter-view {
    max-width: 100% !important;
    margin: 0 !important;
    padding: 0 !important;
  }
  .chapter-header {
    border-bottom: 2px solid #111827 !important;
    padding-bottom: 12px !important;
    margin-bottom: 20px !important;
  }
  .chapter-header h1 {
    color: #111827 !important;
    font-size: 22pt !important;
  }
  .chapter-header p {
    color: #4b5563 !important;
  }
  .chapter-header-tag {
    color: #4f46e5 !important;
  }
  .content-body h2 {
    color: #111827 !important;
    border-bottom: 1px solid #e5e7eb !important;
    page-break-after: avoid;
    break-after: avoid;
    margin-top: 20pt !important;
  }
  .content-body h3 {
    color: #1f2937 !important;
    page-break-after: avoid;
    break-after: avoid;
  }
  .content-body p, .content-body li {
    color: #1f2937 !important;
  }
  .box-teacher, .box-concept, .box-example, .box-tip, .box-trap {
    background: #f9fafb !important;
    color: #1f2937 !important;
    border: 1px solid #d1d5db !important;
    page-break-inside: avoid;
    break-inside: avoid;
    margin: 12pt 0 !important;
    padding: 10pt 12pt !important;
  }
  .box-teacher { border-left: 5px solid #4f46e5 !important; }
  .box-concept { border-left: 5px solid #2563eb !important; }
  .box-example { border-left: 5px solid #059669 !important; }
  .box-tip { border-left: 5px solid #d97706 !important; }
  .box-trap { border-left: 5px solid #dc2626 !important; }
  
  .katex {
    color: #111827 !important;
    font-size: 1.05em !important;
  }
  .katex-display {
    page-break-inside: avoid;
    break-inside: avoid;
    margin: 10pt 0 !important;
  }
  pre, code {
    background: #f3f4f6 !important;
    color: #111827 !important;
    border: 1px solid #e5e7eb !important;
    font-family: 'JetBrains Mono', monospace !important;
  }
  pre {
    page-break-inside: avoid;
    break-inside: avoid;
  }
  table {
    border-collapse: collapse !important;
    width: 100% !important;
    page-break-inside: avoid;
    break-inside: avoid;
  }
  th, td {
    border: 1px solid #d1d5db !important;
    color: #111827 !important;
    padding: 5pt 7pt !important;
  }
  th {
    background: #f3f4f6 !important;
  }
}

/* ── Data Management Modal (Backup, Restore, Reset) ── */
.data-modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.75);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 1000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.data-modal-backdrop.open {
  display: flex;
}

.data-modal-box {
  background: #121217;
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  width: 95%;
  max-width: 580px;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.8), 0 0 30px rgba(129, 140, 248, 0.15);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: modalSlideDown 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.data-modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px 24px;
  border-bottom: 1px solid var(--border-subtle);
  background: var(--bg-card);
}

.data-modal-header h2 {
  font-size: 17px;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.data-modal-body {
  padding: 24px;
}

.data-action-group {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.data-action-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px 16px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
}

.data-action-item.danger {
  border-color: rgba(248, 113, 113, 0.3);
  background: rgba(248, 113, 113, 0.05);
}

.data-action-title {
  font-size: 13.5px;
  font-weight: 600;
  color: var(--text-primary);
}

.data-action-desc {
  font-size: 11.5px;
  color: var(--text-muted);
  margin-top: 2px;
}

.btn-secondary-action {
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  color: var(--text-primary);
  font-size: 13px;
  font-weight: 500;
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn-secondary-action:hover {
  background: var(--border-default);
}

.btn-danger-action {
  background: rgba(248, 113, 113, 0.15);
  border: 1px solid var(--error);
  color: var(--error);
  font-size: 13px;
  font-weight: 600;
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn-danger-action:hover {
  background: var(--error);
  color: #ffffff;
}

/* ── Top Bar & Chapter Back Buttons ── */
.btn-topbar-back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(129, 140, 248, 0.12);
  border: 1px solid rgba(129, 140, 248, 0.28);
  color: #c7d2fe;
  font-size: 12.5px;
  font-weight: 600;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
  white-space: nowrap;
}
.btn-topbar-back:hover {
  background: var(--accent-indigo);
  color: #ffffff;
  border-color: var(--accent-indigo);
  transform: translateX(-2px);
  box-shadow: 0 4px 12px rgba(129, 140, 248, 0.35);
}
.btn-back-arrow {
  font-size: 14px;
  line-height: 1;
}

.btn-chapter-back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  color: var(--text-secondary);
  font-size: 12px;
  font-weight: 500;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  margin-bottom: 14px;
  transition: all var(--transition-fast);
}
.btn-chapter-back:hover {
  background: var(--bg-card-hover);
  color: var(--accent-indigo);
  border-color: var(--accent-indigo);
  transform: translateX(-2px);
}

/* ── 2 Distinct Curricular Sections ── */
.curriculum-tier-banner {
  padding: 20px 24px;
  border-radius: var(--radius-lg);
  margin-bottom: 20px;
  position: relative;
  overflow: hidden;
  border: 1px solid var(--border-default);
}
.curriculum-tier-banner.tier-theory {
  background: linear-gradient(135deg, rgba(129, 140, 248, 0.12) 0%, rgba(30, 27, 75, 0.25) 100%);
  border-color: rgba(129, 140, 248, 0.28);
  box-shadow: 0 8px 24px rgba(99, 102, 241, 0.08);
}
.curriculum-tier-banner.tier-lab {
  background: linear-gradient(135deg, rgba(56, 189, 248, 0.12) 0%, rgba(14, 116, 144, 0.2) 50%, rgba(232, 121, 249, 0.1) 100%);
  border-color: rgba(56, 189, 248, 0.35);
  box-shadow: 0 8px 24px rgba(56, 189, 248, 0.12);
}
.tier-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 4px 10px;
  border-radius: 999px;
  background: rgba(129, 140, 248, 0.2);
  color: #c7d2fe;
  border: 1px solid rgba(129, 140, 248, 0.4);
  margin-bottom: 8px;
}
.tier-badge.lab-badge {
  background: rgba(56, 189, 248, 0.2);
  color: #7dd3fc;
  border-color: rgba(56, 189, 248, 0.4);
}
.tier-title {
  font-size: 18px;
  font-weight: 700;
  color: var(--text-primary);
  margin: 0 0 6px 0;
}
.tier-title.lab-title {
  color: #e0f2fe;
}
.tier-desc {
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.5;
  margin: 0;
}

/* Distinct Card styling for Lab Tier */
.subject-card.tier-lab-card {
  border-color: rgba(56, 189, 248, 0.25);
  background: linear-gradient(180deg, rgba(18, 18, 23, 0.95) 0%, rgba(12, 28, 48, 0.5) 100%);
}
.subject-card.tier-lab-card:hover {
  border-color: rgba(56, 189, 248, 0.6);
  box-shadow: 0 12px 30px rgba(56, 189, 248, 0.18);
}

/* Sidebar Sections */
.sidebar-section-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 14px 16px 6px 16px;
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}
.sidebar-section-header.theory-header {
  color: #a5b4fc;
}
.sidebar-section-header.lab-header {
  color: #38bdf8;
  margin-top: 10px;
}
.sidebar-section-tag {
  margin-left: auto;
  font-size: 9.5px;
  padding: 2px 6px;
  border-radius: 4px;
  background: rgba(56, 189, 248, 0.15);
  color: #7dd3fc;
  border: 1px solid rgba(56, 189, 248, 0.3);
}
.sidebar-section-divider {
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--border-default), transparent);
  margin: 12px 14px;
}

/* ── Text-to-Speech (TTS) Engine Styling ── */
.tts-speaking-target {
  position: relative;
  border-color: rgba(129, 140, 248, 0.45) !important;
  background: rgba(129, 140, 248, 0.03) !important;
  box-shadow: 0 0 28px rgba(129, 140, 248, 0.18);
  transition: all 0.35s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ── Interactive Sentence & Line Hover Affordance ── */
.tts-sentence {
  display: inline;
  border-radius: 4px;
  cursor: pointer;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
  transition: background-color 0.2s ease, box-shadow 0.2s ease;
}

.tts-sentence:hover:not(.active-speaking) {
  background-color: rgba(129, 140, 248, 0.10);
  box-shadow: 0 0 8px rgba(129, 140, 248, 0.18);
}

/* ── Active Speaking Line & Sentence Interface ── */
.active-speaking,
.tts-sentence.active-speaking {
  position: relative;
  display: inline;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
  background: linear-gradient(90deg, rgba(99, 102, 241, 0.22) 0%, rgba(168, 85, 247, 0.16) 45%, rgba(56, 189, 248, 0.10) 100%);
  border-left: 4px solid #818cf8;
  outline: 1.5px solid rgba(168, 85, 247, 0.65);
  outline-offset: 1.5px;
  border-radius: 6px;
  padding: 3px 8px 3px 6px;
  margin: 0 2px;
  box-shadow: 0 0 18px rgba(129, 140, 248, 0.42), 0 0 36px rgba(99, 102, 241, 0.18), inset 0 0 10px rgba(129, 140, 248, 0.15);
  animation: activeSpeakingPulse 2.8s ease-in-out infinite;
  transform: scale(1.01) translateZ(0);
  transform-origin: left center;
  transition: transform 0.35s cubic-bezier(0.2, 0.8, 0.2, 1),
              box-shadow 0.35s ease,
              background 0.35s ease,
              border-color 0.35s ease,
              outline-color 0.35s ease,
              color 0.2s ease;
  z-index: 2;
  color: #ffffff;
  filter: drop-shadow(0 0 6px rgba(129, 140, 248, 0.35));
}

/* Soft animated aura behind active lines */
.active-speaking::before,
.tts-sentence.active-speaking::before {
  content: '';
  position: absolute;
  inset: -4px -8px;
  border-radius: inherit;
  background: radial-gradient(ellipse at 50% 50%, rgba(129, 140, 248, 0.32) 0%, rgba(168, 85, 247, 0.18) 45%, rgba(56, 189, 248, 0.08) 75%, transparent 100%);
  z-index: -1;
  pointer-events: none;
  filter: blur(5px);
  animation: activeAuraBreathe 3.4s ease-in-out infinite alternate;
  transition: opacity 0.35s ease, transform 0.35s ease;
}

/* Block-level active speaking targets (<p>, <li>, <h3>, formulas, etc.) */
p.active-speaking,
li.active-speaking,
h1.active-speaking,
h2.active-speaking,
h3.active-speaking,
h4.active-speaking,
h5.active-speaking,
h6.active-speaking,
div.active-speaking,
blockquote.active-speaking,
tr.active-speaking {
  display: block;
  padding: 12px 16px 12px 16px;
  margin-top: 8px;
  margin-bottom: 8px;
  border: 1.5px solid rgba(168, 85, 247, 0.85);
  border-left: 5px solid #818cf8;
  outline: 1.5px solid rgba(129, 140, 248, 0.45);
  outline-offset: 2px;
  border-radius: 12px;
  transform: scale(1.01) translateZ(0);
}

@keyframes activeSpeakingPulse {
  0%, 100% {
    box-shadow: 0 0 16px rgba(129, 140, 248, 0.38),
                0 0 32px rgba(99, 102, 241, 0.16),
                inset 0 0 10px rgba(129, 140, 248, 0.14);
    border-color: rgba(129, 140, 248, 0.75);
    outline-color: rgba(168, 85, 247, 0.6);
  }
  50% {
    box-shadow: 0 0 28px rgba(129, 140, 248, 0.6),
                0 0 54px rgba(168, 85, 247, 0.3),
                inset 0 0 18px rgba(129, 140, 248, 0.24);
    border-color: rgba(192, 132, 252, 0.98);
    outline-color: rgba(129, 140, 248, 0.9);
  }
}

@keyframes activeAuraBreathe {
  0% {
    opacity: 0.65;
    transform: scale(0.992);
  }
  100% {
    opacity: 1;
    transform: scale(1.018);
  }
}

/* ── Animated Equalizer / Waveform Indicator (5-Bar Waveform) ── */
.tts-active-equalizer {
  display: inline-flex;
  align-items: flex-end;
  gap: 2.5px;
  height: 18px;
  margin-right: 8px;
  vertical-align: middle;
  padding: 2px 5px;
  background: rgba(15, 23, 42, 0.75);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border: 1px solid rgba(129, 140, 248, 0.45);
  border-radius: 6px;
  box-shadow: 0 0 12px rgba(129, 140, 248, 0.25);
  pointer-events: none;
  user-select: none;
  transition: all 0.35s ease;
}

.tts-active-equalizer .eq-bar {
  display: block;
  width: 2.5px;
  min-height: 3px;
  background: linear-gradient(to top, #6366f1, #a855f7, #38bdf8);
  border-radius: 2px;
  animation-duration: 0.9s;
  animation-iteration-count: infinite;
  animation-timing-function: cubic-bezier(0.4, 0, 0.2, 1);
}

.tts-active-equalizer .bar-1 {
  height: 6px;
  animation-name: eqBounce1;
  animation-delay: 0.05s;
}
.tts-active-equalizer .bar-2 {
  height: 13px;
  animation-name: eqBounce2;
  animation-delay: 0.22s;
}
.tts-active-equalizer .bar-3 {
  height: 16px;
  animation-name: eqBounce3;
  animation-delay: 0.12s;
}
.tts-active-equalizer .bar-4 {
  height: 9px;
  animation-name: eqBounce4;
  animation-delay: 0.32s;
}
.tts-active-equalizer .bar-5 {
  height: 14px;
  animation-name: eqBounce5;
  animation-delay: 0.18s;
}

@keyframes eqBounce1 {
  0%, 100% { height: 4px; }
  50% { height: 14px; }
}
@keyframes eqBounce2 {
  0%, 100% { height: 14px; }
  50% { height: 5px; }
}
@keyframes eqBounce3 {
  0%, 100% { height: 6px; }
  50% { height: 17px; }
}
@keyframes eqBounce4 {
  0%, 100% { height: 12px; }
  50% { height: 4px; }
}
@keyframes eqBounce5 {
  0%, 100% { height: 5px; }
  50% { height: 15px; }
}

/* ── Paused State Styling (Warm Amber Aura & Frozen Bars) ── */
.active-speaking.is-paused,
body.tts-paused .active-speaking {
  animation: none !important;
  border-color: rgba(245, 158, 11, 0.85) !important;
  border-left-color: #f59e0b !important;
  outline-color: rgba(245, 158, 11, 0.65) !important;
  background: linear-gradient(90deg, rgba(245, 158, 11, 0.18) 0%, rgba(217, 119, 6, 0.08) 100%) !important;
  box-shadow: 0 0 22px rgba(245, 158, 11, 0.38), inset 0 0 10px rgba(245, 158, 11, 0.14) !important;
  filter: drop-shadow(0 0 6px rgba(245, 158, 11, 0.25)) !important;
}

.active-speaking.is-paused::before,
body.tts-paused .active-speaking::before {
  animation: none !important;
  background: radial-gradient(ellipse at 50% 50%, rgba(245, 158, 11, 0.24) 0%, rgba(217, 119, 6, 0.12) 50%, transparent 80%) !important;
  opacity: 0.85 !important;
}

.active-speaking.is-paused .tts-active-equalizer,
body.tts-paused .active-speaking .tts-active-equalizer {
  background: rgba(30, 20, 10, 0.85) !important;
  border-color: rgba(245, 158, 11, 0.5) !important;
  box-shadow: 0 0 10px rgba(245, 158, 11, 0.25) !important;
}

.active-speaking.is-paused .tts-active-equalizer .eq-bar,
body.tts-paused .active-speaking .tts-active-equalizer .eq-bar {
  animation-play-state: paused !important;
  background: linear-gradient(to top, #f59e0b, #fbbf24) !important;
}

/* ── Native Word Highlight (W3C CSS.highlights) ── */
::highlight(tts-word-highlight) {
  background-color: rgba(255, 255, 255, 0.28);
  color: #ffffff;
  border-radius: 3px;
  text-shadow: 0 0 8px rgba(129, 140, 248, 0.6);
}

/* ── Light Mode Support ── */
[data-theme="light"] .active-speaking,
body.light-theme .active-speaking,
body.light-mode .active-speaking {
  background: linear-gradient(90deg, rgba(79, 70, 229, 0.14) 0%, rgba(147, 51, 234, 0.10) 50%, rgba(14, 165, 233, 0.07) 100%);
  border-color: rgba(79, 70, 229, 0.8);
  border-left-color: #4f46e5;
  outline-color: rgba(147, 51, 234, 0.5);
  color: #0f172a;
  box-shadow: 0 0 20px rgba(79, 70, 229, 0.28), 0 4px 12px rgba(0, 0, 0, 0.06);
  filter: drop-shadow(0 0 4px rgba(79, 70, 229, 0.25));
}

[data-theme="light"] .active-speaking::before,
body.light-theme .active-speaking::before,
body.light-mode .active-speaking::before {
  background: radial-gradient(ellipse at 50% 50%, rgba(79, 70, 229, 0.20) 0%, rgba(147, 51, 234, 0.10) 45%, transparent 80%);
}

[data-theme="light"] .tts-active-equalizer,
body.light-theme .tts-active-equalizer,
body.light-mode .tts-active-equalizer {
  background: rgba(255, 255, 255, 0.92);
  border-color: rgba(79, 70, 229, 0.35);
  box-shadow: 0 2px 8px rgba(79, 70, 229, 0.18);
}

[data-theme="light"] .tts-active-equalizer .eq-bar,
body.light-theme .tts-active-equalizer .eq-bar,
body.light-mode .tts-active-equalizer .eq-bar {
  background: linear-gradient(to top, #4f46e5, #9333ea);
}

[data-theme="light"] ::highlight(tts-word-highlight),
body.light-theme ::highlight(tts-word-highlight),
body.light-mode ::highlight(tts-word-highlight) {
  background-color: rgba(79, 70, 229, 0.35);
  color: #0f172a;
  text-shadow: none;
}

.tts-box-toolbar {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-left: auto;
  flex-wrap: wrap;
}

.tts-play-btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  background: rgba(255, 255, 255, 0.06);
  border: 1px solid rgba(255, 255, 255, 0.12);
  color: var(--text-secondary);
  font-size: 11.5px;
  font-weight: 600;
  padding: 4px 10px;
  border-radius: 999px;
  cursor: pointer;
  transition: all var(--transition-fast);
  user-select: none;
}
.tts-play-btn:hover {
  background: rgba(129, 140, 248, 0.2);
  border-color: rgba(129, 140, 248, 0.5);
  color: #ffffff;
  transform: translateY(-1px);
}
.tts-play-btn.playing {
  background: var(--accent-indigo);
  border-color: var(--accent-indigo);
  color: #ffffff;
  box-shadow: 0 0 12px rgba(129, 140, 248, 0.4);
  animation: ttsPulse 1.8s infinite;
}

.tts-inline-btn {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid rgba(255, 255, 255, 0.12);
  color: var(--text-secondary);
  font-size: 11px;
  font-weight: 600;
  padding: 2px 8px;
  border-radius: 999px;
  cursor: pointer;
  margin-left: 8px;
  vertical-align: middle;
  transition: all var(--transition-fast);
  user-select: none;
}
.tts-inline-btn:hover {
  background: rgba(129, 140, 248, 0.2);
  border-color: rgba(129, 140, 248, 0.5);
  color: #fff;
  transform: translateY(-1px);
}
.tts-inline-btn.tts-inline-q:hover {
  background: rgba(251, 191, 36, 0.15);
  border-color: #fbbf24;
  color: #fef08a;
}
.tts-inline-btn.tts-inline-a:hover {
  background: rgba(52, 211, 153, 0.15);
  border-color: #34d399;
  color: #a7f3d0;
}
.tts-inline-btn.playing {
  background: var(--accent-indigo);
  border-color: var(--accent-indigo);
  color: #ffffff;
  box-shadow: 0 0 10px rgba(129, 140, 248, 0.4);
}
@keyframes ttsPulse {
  0% { box-shadow: 0 0 0 0 rgba(129, 140, 248, 0.6); }
  70% { box-shadow: 0 0 0 8px rgba(129, 140, 248, 0); }
  100% { box-shadow: 0 0 0 0 rgba(129, 140, 248, 0); }
}

.tts-play-btn.tts-btn-q:hover {
  border-color: #fbbf24;
  color: #fef08a;
  background: rgba(251, 191, 36, 0.15);
}
.tts-play-btn.tts-btn-a:hover {
  border-color: #34d399;
  color: #a7f3d0;
  background: rgba(52, 211, 153, 0.15);
}

.tts-section-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  background: transparent;
  border: none;
  font-size: 15px;
  cursor: pointer;
  margin-left: 8px;
  opacity: 0.6;
  vertical-align: middle;
  padding: 4px;
  border-radius: 4px;
  transition: opacity 0.2s, transform 0.2s;
}
.tts-section-btn:hover {
  opacity: 1;
  transform: scale(1.15);
}

.tts-chapter-header-btn {
  background: rgba(129, 140, 248, 0.15);
  border: 1px solid rgba(129, 140, 248, 0.3);
  color: #c7d2fe;
}
.tts-chapter-header-btn:hover {
  background: var(--accent-indigo);
  color: #ffffff;
  border-color: var(--accent-indigo);
  box-shadow: 0 4px 14px rgba(129, 140, 248, 0.3);
}

/* ── Floating TTS Player Bar ── */
.tts-floating-player {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(120px);
  background: rgba(18, 18, 24, 0.95);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid rgba(129, 140, 248, 0.35);
  border-radius: 999px;
  box-shadow: 0 16px 40px rgba(0, 0, 0, 0.75), 0 0 25px rgba(129, 140, 248, 0.2);
  z-index: 1050;
  padding: 8px 18px;
  transition: transform 0.35s cubic-bezier(0.16, 1, 0.3, 1), opacity 0.3s ease;
  opacity: 0;
  pointer-events: none;
  max-width: 95vw;
}

.tts-floating-player.active {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
  pointer-events: auto;
}

.tts-player-inner {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: nowrap;
}

.tts-player-info {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 140px;
  max-width: 220px;
}

.tts-player-wave {
  display: flex;
  align-items: flex-end;
  gap: 2.5px;
  height: 16px;
  width: 16px;
}
.tts-player-wave span {
  display: block;
  width: 2.5px;
  height: 4px;
  background: var(--accent-indigo);
  border-radius: 2px;
}
.tts-player-wave.animating span:nth-child(1) { animation: waveAnim 1s ease-in-out infinite 0.1s; }
.tts-player-wave.animating span:nth-child(2) { animation: waveAnim 1s ease-in-out infinite 0.3s; }
.tts-player-wave.animating span:nth-child(3) { animation: waveAnim 1s ease-in-out infinite 0.2s; }
.tts-player-wave.animating span:nth-child(4) { animation: waveAnim 1s ease-in-out infinite 0.4s; }

@keyframes waveAnim {
  0%, 100% { height: 4px; }
  50% { height: 16px; }
}

.tts-player-title-wrap {
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
.tts-player-status {
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent-indigo);
  font-weight: 700;
}
.tts-player-title {
  font-size: 12px;
  color: var(--text-primary);
  font-weight: 600;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.tts-player-controls {
  display: flex;
  align-items: center;
  gap: 6px;
}

.tts-ctrl-btn {
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  color: var(--text-primary);
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 13px;
  cursor: pointer;
  transition: all var(--transition-fast);
}
.tts-ctrl-btn:hover {
  background: var(--accent-indigo);
  color: #ffffff;
  border-color: var(--accent-indigo);
  transform: scale(1.08);
}
.tts-ctrl-btn.tts-ctrl-playpause {
  background: var(--accent-indigo);
  color: #ffffff;
  border-color: var(--accent-indigo);
  width: 36px;
  height: 36px;
  font-size: 15px;
}
.tts-ctrl-btn.tts-ctrl-playpause:hover {
  transform: scale(1.1);
  box-shadow: 0 0 14px rgba(129, 140, 248, 0.5);
}

.tts-player-settings {
  display: flex;
  align-items: center;
  gap: 12px;
}

.tts-speed-picker {
  display: flex;
  gap: 4px;
  background: rgba(255, 255, 255, 0.05);
  padding: 3px;
  border-radius: 999px;
}
.tts-speed-chip {
  background: transparent;
  border: none;
  color: var(--text-secondary);
  font-size: 11px;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: 999px;
  cursor: pointer;
  transition: all 0.15s;
}
.tts-speed-chip:hover {
  color: #ffffff;
}
.tts-speed-chip.active {
  background: var(--accent-indigo);
  color: #ffffff;
}

.tts-vol-wrap {
  display: flex;
  align-items: center;
  gap: 6px;
}
.tts-vol-icon {
  font-size: 13px;
  color: var(--text-muted);
}
#tts-vol-slider {
  width: 60px;
  height: 4px;
  accent-color: var(--accent-indigo);
  cursor: pointer;
}

.tts-close-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  font-size: 13px;
  cursor: pointer;
  padding: 4px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: color 0.2s;
}
.tts-close-btn:hover {
  color: var(--error);
}

.tts-toast {
  position: fixed;
  bottom: 84px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: #1f1f28;
  color: var(--text-primary);
  border: 1px solid var(--border-default);
  padding: 10px 20px;
  border-radius: var(--radius-md);
  font-size: 13px;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  pointer-events: none;
  transition: all 0.25s ease;
  z-index: 1060;
}
.tts-toast.visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* Mobile adjustments for TTS & Tiers */
@media (max-width: 768px) {
  .tts-floating-player {
    bottom: 12px;
    padding: 8px 12px;
    border-radius: 16px;
    width: 96vw;
  }
  .tts-player-inner {
    flex-wrap: wrap;
    gap: 8px;
    justify-content: space-between;
  }
  .tts-player-info {
    max-width: 100%;
    flex: 1 1 100%;
  }
  .tts-vol-wrap {
    display: none;
  }
  .curriculum-tier-banner {
    padding: 16px;
  }
  .btn-topbar-back .btn-back-text {
    display: none;
  }

  /* Active Speaking Mobile Adjustments */
  .active-speaking,
  .tts-sentence.active-speaking {
    transform: scale(1.004) translateZ(0);
    margin: 0 1px;
    padding: 2px 6px 2px 5px;
  }
  p.active-speaking,
  li.active-speaking,
  h1.active-speaking,
  h2.active-speaking,
  h3.active-speaking,
  h4.active-speaking,
  h5.active-speaking,
  h6.active-speaking,
  div.active-speaking,
  blockquote.active-speaking,
  tr.active-speaking {
    padding: 10px 12px;
    border-left-width: 4px;
    transform: scale(1.004) translateZ(0);
  }
  .tts-active-equalizer {
    height: 15px;
    gap: 2px;
    margin-right: 6px;
    padding: 1px 4px;
  }
  .tts-active-equalizer .eq-bar {
    width: 2px;
  }

  /* Formula Hub Mobile Fixes (Zero Label Overlap) */
  .formula-modal-backdrop {
    padding: 10px;
  }
  .formula-modal-box {
    width: 100%;
    max-height: 94vh;
    border-radius: 12px;
  }
  .formula-modal-header {
    padding: 12px 14px;
    gap: 10px;
  }
  .formula-modal-header h2 {
    font-size: 14px;
  }
  .formula-subject-tabs {
    padding: 8px 12px;
    gap: 6px;
  }
  .formula-tab-btn {
    padding: 6px 12px;
    font-size: 11.5px;
    min-height: 34px;
  }
  .formula-content-scroll {
    padding: 14px 10px;
  }
  .formula-grid {
    grid-template-columns: 1fr;
    gap: 12px;
  }
  .formula-card {
    padding: 12px 14px;
  }
  .formula-card-title {
    font-size: 13px;
  }
}

/* ── Accessibility: Prefers Reduced Motion (WCAG 2.2) ── */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
  .active-speaking,
  .tts-sentence.active-speaking,
  p.active-speaking,
  li.active-speaking,
  h1.active-speaking,
  h2.active-speaking,
  h3.active-speaking,
  h4.active-speaking,
  h5.active-speaking,
  h6.active-speaking,
  div.active-speaking,
  blockquote.active-speaking,
  tr.active-speaking {
    animation: none !important;
    transform: none !important;
    transition: none !important;
  }
  .active-speaking::before,
  .tts-sentence.active-speaking::before,
  p.active-speaking::before,
  li.active-speaking::before,
  h1.active-speaking::before,
  h2.active-speaking::before,
  h3.active-speaking::before,
  h4.active-speaking::before,
  div.active-speaking::before,
  blockquote.active-speaking::before {
    animation: none !important;
    transform: none !important;
  }
  .tts-active-equalizer .eq-bar {
    animation: none !important;
    height: 8px !important;
  }
}