@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500;600&family=Outfit:wght@400;500;600;700;800&display=swap');

:root {
  --bg-primary: #0a0e27;
  --bg-secondary: #111638;
  --bg-card: rgba(255, 255, 255, 0.04);
  --bg-glass: rgba(255, 255, 255, 0.06);
  --text-primary: #e8eaf6;
  --text-secondary: #9fa4c4;
  --text-muted: #9ea3c7;
  --accent-primary: #fbbf24;
  --accent-light: #fcd34d;
  --accent-amber: #f59e0b;
  --accent-teal: #06b6d4;
  --accent-green: #10b981;
  --accent-rose: #f43f5e;
  --accent-purple: #8b5cf6;
  --gradient-hero: linear-gradient(135deg, #d97706 0%, #fbbf24 100%);
  --gradient-warm: linear-gradient(135deg, #b45309 0%, #d97706 100%);
  --shadow-lg: 0 20px 60px rgba(0, 0, 0, 0.4);
  --shadow-glow: 0 0 30px rgba(251, 191, 36, 0.3);
  --radius: 16px;
  --radius-sm: 10px;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.8;
  min-height: 100vh;
  overflow-x: hidden;
  user-select: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
}

img {
  -webkit-user-drag: none;
}

h1,
h2,
h3,
h4,
h5 {
  font-family: 'Outfit', sans-serif;
  line-height: 1.3;
}

/* ===== PARTICLES BACKGROUND ===== */
#particles-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
  pointer-events: none;
  opacity: 0.4;
}

/* ===== SIDEBAR NAV ===== */
.sidebar {
  position: fixed;
  left: 0;
  top: 0;
  width: 300px;
  height: 100vh;
  background: var(--bg-secondary);
  border-right: 1px solid rgba(255, 255, 255, 0.06);
  z-index: 100;
  display: flex;
  flex-direction: column;
  transition: transform var(--transition);
  overflow-y: auto;
}

.sidebar.collapsed {
  transform: translateX(-300px);
}

.sidebar-header {
  padding: 24px 20px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
  display: flex;
  align-items: center;
  gap: 12px;
}

.sidebar-header img {
  width: 44px;
  height: 44px;
  border-radius: 12px;
  object-fit: cover;
}

.sidebar-header h2 {
  font-size: 1.05rem;
  font-weight: 700;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.sidebar-header span {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.nav-list {
  list-style: none;
  padding: 12px 10px;
  flex: 1;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 11px 16px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  margin-bottom: 2px;
  position: relative;
}

.nav-item:hover {
  background: var(--bg-glass);
  color: var(--text-primary);
}

.nav-item.active {
  background: rgba(251, 191, 36, 0.15);
  color: #fcd34d;
}

.nav-item.active::before {
  content: '';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  width: 3px;
  height: 60%;
  background: var(--accent-primary);
  border-radius: 4px;
}

.nav-num {
  width: 28px;
  height: 28px;
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 700;
  background: var(--bg-glass);
  flex-shrink: 0;
  font-family: 'JetBrains Mono', monospace;
}

.nav-item.active .nav-num {
  background: rgba(251, 191, 36, 0.3);
  color: #fcd34d;
}

/* Part dividers in sidebar */
.nav-part-divider {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 14px 16px 6px;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent-primary);
  opacity: 0.7;
  margin-top: 8px;
}

.nav-part-divider::after {
  content: '';
  flex: 1;
  height: 1px;
  background: rgba(251, 191, 36, 0.2);
}

/* ===== LANGUAGE SWITCHER ===== */
.lang-switcher {
  display: flex;
  gap: 0.25rem;
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 10px;
  padding: 0.25rem;
  margin: 0.75rem 1rem 0;
}

.lang-btn {
  flex: 1;
  background: transparent;
  border: none;
  color: var(--text-muted);
  font-family: 'Outfit', 'Inter', sans-serif;
  font-size: 0.78rem;
  font-weight: 600;
  padding: 0.4rem 0.6rem;
  border-radius: 7px;
  cursor: pointer;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  white-space: nowrap;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.lang-btn:hover {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.07);
}

.lang-btn.active {
  background: linear-gradient(135deg, #d97706, #fbbf24);
  color: #fff;
  box-shadow: 0 2px 12px rgba(251, 191, 36, 0.35);
}

.lang-btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at var(--ripple-x, 50%) var(--ripple-y, 50%), rgba(255, 255, 255, 0.25) 0%, transparent 60%);
  opacity: 0;
  transition: opacity 0.4s ease;
  pointer-events: none;
}

.lang-btn:active::after {
  opacity: 1;
  transition: opacity 0s;
}

/* ===== MOBILE NAV TOGGLE ===== */
.nav-toggle {
  position: fixed;
  top: 16px;
  left: 16px;
  z-index: 200;
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: var(--bg-secondary);
  border: 1px solid rgba(255, 255, 255, 0.1);
  color: var(--text-primary);
  cursor: pointer;
  display: none;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
}

.nav-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  z-index: 99;
  opacity: 0;
  transition: opacity var(--transition);
}

.nav-overlay.show {
  display: block;
  opacity: 1;
}

/* ===== MAIN CONTENT ===== */
.main-content {
  margin-left: 300px;
  position: relative;
  z-index: 1;
  min-height: 100vh;
  transition: margin-left var(--transition);
}

.main-content.expanded {
  margin-left: 0;
}

/* ===== CHAPTER CONTENT ===== */
.chapter {
  display: none;
  animation: fadeIn 0.5s ease;
}

.chapter.active {
  display: block;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.chapter-hero {
  position: relative;
  overflow: hidden;
}

.chapter-hero img {
  max-width: 100%;
  max-height: 100vh;
  /* width: auto; */
  width: 100%;
  height: auto;
  display: block;
  margin: 0 auto;
}

.chapter-hero-overlay {
  position: relative;
  z-index: 2;
  padding: 32px 48px 36px;
  width: 100%;
  background: linear-gradient(to bottom, rgba(10, 14, 39, 0.85) 0%, var(--bg-primary) 100%);
  margin-top: -40px;
}

.chapter-hero-overlay .ch-num {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.8rem;
  color: var(--accent-amber);
  font-weight: 600;
  letter-spacing: 3px;
  text-transform: uppercase;
  margin-bottom: 8px;
}

.chapter-hero-overlay h1 {
  font-size: 2.6rem;
  font-weight: 800;
  margin-bottom: 8px;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.chapter-hero-overlay .ch-subtitle {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 600px;
}

.chapter-body {
  max-width: 860px;
  margin: 0 auto;
  padding: 48px 32px 80px;
}

.chapter-body h2 {
  font-size: 1.7rem;
  font-weight: 700;
  margin: 48px 0 20px;
  color: var(--text-primary);
  position: relative;
  padding-left: 20px;
}

.chapter-body h2::before {
  content: '';
  position: absolute;
  left: 0;
  top: 4px;
  width: 4px;
  height: 28px;
  background: var(--gradient-hero);
  border-radius: 4px;
}

.chapter-body h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 32px 0 14px;
  color: var(--accent-light);
}

.chapter-body p {
  margin-bottom: 18px;
  color: var(--text-secondary);
  font-size: 1.02rem;
}

/* ===== STORY DIALOGUE ===== */
.dialogue {
  display: flex;
  gap: 16px;
  margin: 24px 0;
  padding: 20px;
  background: var(--bg-glass);
  border-radius: var(--radius);
  border: 1px solid rgba(255, 255, 255, 0.06);
}

.dialogue-avatar {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.1rem;
}

.dialogue-avatar.ava {
  background: linear-gradient(135deg, #7c3aed, #a78bfa);
  color: #fff;
}

.dialogue-avatar.max {
  background: linear-gradient(135deg, #d97706, #fbbf24);
  color: #fff;
}

.dialogue-content {
  flex: 1;
}

.dialogue-name {
  font-weight: 700;
  font-size: 0.85rem;
  margin-bottom: 4px;
}

.dialogue-name.ava {
  color: #a78bfa;
}

.dialogue-name.max {
  color: var(--accent-primary);
}

.dialogue-text {
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.7;
}

/* ===== CODE BLOCKS ===== */
.code-block {
  margin: 24px 0;
  border-radius: var(--radius);
  background: #0d1117;
  border: 1px solid rgba(255, 255, 255, 0.08);
  overflow: hidden;
}

.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 16px;
  background: rgba(255, 255, 255, 0.04);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
}

.code-lang {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  color: var(--accent-primary);
  font-weight: 600;
  text-transform: uppercase;
}

.code-copy {
  background: none;
  border: 1px solid rgba(255, 255, 255, 0.1);
  color: var(--text-muted);
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.72rem;
  cursor: pointer;
  transition: var(--transition);
}

.code-copy:hover {
  border-color: var(--accent-primary);
  color: var(--accent-light);
}

.code-block pre {
  padding: 20px;
  overflow-x: auto;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.88rem;
  line-height: 1.7;
  color: #c9d1d9;
}

/* ===== SYNTAX HIGHLIGHTING ===== */
.kw {
  color: #ff7b72;
}

.fn {
  color: #d2a8ff;
}

.str {
  color: #a5d6ff;
}

.num {
  color: #79c0ff;
}

.cmt {
  color: #6b7b8d;
  font-style: italic;
}

.op {
  color: #ff7b72;
}

.type {
  color: #ffa657;
}

.var {
  color: #ffa657;
}

.tag {
  color: #7ee787;
}

.attr {
  color: #79c0ff;
}

.val {
  color: #a5d6ff;
}

/* ===== CONCEPT CARDS ===== */
.concept-card {
  margin: 28px 0;
  padding: 24px 28px;
  border-radius: var(--radius);
  background: var(--bg-glass);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-left: 4px solid var(--accent-primary);
}

.concept-card.tip {
  border-left-color: var(--accent-green);
}

.concept-card.warning {
  border-left-color: var(--accent-amber);
}

.concept-card.info {
  border-left-color: var(--accent-primary);
}

.concept-card h4 {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.concept-card p {
  margin-bottom: 8px;
  font-size: 0.95rem;
}

/* ===== FLOWCHARTS (MERMAID) ===== */
.flowchart-container {
  margin: 32px 0;
  padding: 28px;
  background: rgba(255, 255, 255, 0.03);
  border-radius: var(--radius);
  border: 1px solid rgba(255, 255, 255, 0.06);
  text-align: center;
  overflow-x: auto;
}

.flowchart-container h4 {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 16px;
  text-transform: uppercase;
  letter-spacing: 2px;
}

/* Mermaid subgraph & cluster safety — prevent title overlap with top nodes */
.mermaid { line-height: 1.4; }
.mermaid svg { height: auto; min-width: 100%; }
.mermaid .cluster rect { rx: 10; ry: 10; }
.mermaid .cluster-label foreignObject { overflow: visible !important; }
.mermaid .cluster-label .nodeLabel,
.mermaid .cluster-label span {
  background: rgba(10, 6, 30, 0.92);
  padding: 3px 12px;
  border-radius: 6px;
  font-weight: 600;
  white-space: nowrap;
}
.mermaid .nodeLabel { line-height: 1.35; }

/* ===== INLINE IMAGES ===== */
.chapter-img {
  margin: 32px 0;
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid rgba(255, 255, 255, 0.06);
}

.chapter-img img {
  width: 100%;
  display: block;
}

.chapter-img figcaption {
  padding: 12px 16px;
  font-size: 0.82rem;
  color: var(--text-muted);
  text-align: center;
  background: var(--bg-glass);
}

/* ===== QUIZ SECTION ===== */
.quiz-section {
  margin: 40px 0;
  padding: 32px;
  border-radius: var(--radius);
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.08), rgba(217, 119, 6, 0.08));
  border: 1px solid rgba(251, 191, 36, 0.2);
}

.quiz-section h3 {
  color: var(--accent-amber);
  margin-top: 0;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  gap: 10px;
}

.quiz-question {
  margin: 20px 0;
}

.quiz-question p {
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 10px;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.quiz-option {
  padding: 12px 16px;
  border-radius: var(--radius-sm);
  background: var(--bg-glass);
  border: 1px solid rgba(255, 255, 255, 0.08);
  cursor: pointer;
  transition: var(--transition);
  font-size: 0.92rem;
  color: var(--text-secondary);
}

.quiz-option:hover {
  border-color: var(--accent-primary);
  background: rgba(251, 191, 36, 0.1);
}

.quiz-option.correct {
  border-color: var(--accent-green);
  background: rgba(16, 185, 129, 0.15);
  color: var(--accent-green);
}

.quiz-option.wrong {
  border-color: var(--accent-rose);
  background: rgba(244, 63, 94, 0.1);
  color: var(--accent-rose);
}

.quiz-feedback {
  margin-top: 10px;
  padding: 12px;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  display: none;
}

.quiz-feedback.show {
  display: block;
}

.quiz-feedback.correct {
  background: rgba(16, 185, 129, 0.1);
  color: var(--accent-green);
}

.quiz-feedback.wrong {
  background: rgba(244, 63, 94, 0.1);
  color: var(--accent-rose);
}

/* ===== EXERCISE BOX ===== */
.exercise-box {
  margin: 32px 0;
  padding: 28px;
  border-radius: var(--radius);
  background: rgba(251, 191, 36, 0.06);
  border: 1px solid rgba(251, 191, 36, 0.2);
}

.exercise-box h4 {
  color: var(--accent-amber);
  font-size: 1.05rem;
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.exercise-box ol,
.exercise-box ul {
  padding-left: 20px;
  color: var(--text-secondary);
}

.exercise-box li {
  margin-bottom: 8px;
  font-size: 0.95rem;
}

/* ===== COMPARISON TABLE ===== */
.compare-table {
  width: 100%;
  margin: 24px 0;
  border-collapse: collapse;
  border-radius: var(--radius);
  overflow: hidden;
}

.compare-table th {
  padding: 14px 18px;
  background: rgba(251, 191, 36, 0.15);
  color: var(--accent-light);
  font-weight: 600;
  font-size: 0.9rem;
  text-align: left;
}

.compare-table td {
  padding: 12px 18px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.04);
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.compare-table tr:hover td {
  background: var(--bg-glass);
}

.compare-table code {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.82rem;
  background: rgba(0, 0, 0, 0.3);
  padding: 2px 8px;
  border-radius: 4px;
  color: #ffa657;
}

/* ===== CHAPTER NAV FOOTER ===== */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 32px 0;
  margin-top: 48px;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
}

.chapter-nav-btn {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 24px;
  border-radius: var(--radius-sm);
  background: var(--bg-glass);
  border: 1px solid rgba(255, 255, 255, 0.08);
  color: var(--text-secondary);
  cursor: pointer;
  transition: var(--transition);
  font-size: 0.9rem;
  font-weight: 500;
}

.chapter-nav-btn:hover {
  border-color: var(--accent-primary);
  background: rgba(251, 191, 36, 0.1);
}

.chapter-nav-btn.primary {
  background: var(--gradient-hero);
  color: #fff;
  border: none;
  font-weight: 600;
}

.chapter-nav-btn.primary:hover {
  opacity: 0.9;
  transform: translateX(4px);
}

/* ===== COVER PAGE ===== */
.cover-page {
  text-align: center;
  padding: 60px 30px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  position: relative;
}

.vol-marker {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.8rem;
  color: var(--accent-primary);
  text-transform: uppercase;
  letter-spacing: 4px;
  margin-bottom: 24px;
  font-weight: 600;
}

.cover-page img {
  width: min(340px, 80%);
  border-radius: 20px;
  box-shadow: var(--shadow-lg), var(--shadow-glow);
  margin-bottom: 32px;
}

.cover-page h1 {
  font-size: 3.4rem;
  font-weight: 800;
  margin-bottom: 12px;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.cover-page .subtitle {
  max-width: 560px;
  color: var(--text-secondary);
  font-size: 1.05rem;
  line-height: 1.7;
  margin-bottom: 32px;
}

.author-badge {
  position: relative;
  margin: 24px auto 32px;
  max-width: 320px;
}

.author-badge-glow {
  position: absolute;
  inset: -4px;
  border-radius: 20px;
  background: var(--gradient-hero);
  opacity: 0.25;
  filter: blur(16px);
  animation: badgePulse 3s ease-in-out infinite;
}

@keyframes badgePulse {

  0%,
  100% {
    opacity: 0.2;
  }

  50% {
    opacity: 0.35;
  }
}

.author-badge-inner {
  position: relative;
  z-index: 1;
  background: var(--bg-secondary);
  border: 1px solid rgba(251, 191, 36, 0.3);
  border-radius: 16px;
  padding: 18px 24px;
  text-align: center;
}

.author-badge-label {
  display: block;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 3px;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.author-badge-name {
  display: block;
  font-family: 'Outfit', sans-serif;
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
}

.author-badge-links {
  margin-top: 8px;
  display: flex;
  gap: 12px;
  justify-content: center;
}

.author-badge-links a {
  font-size: 0.78rem;
  color: var(--accent-primary);
  text-decoration: none;
  transition: var(--transition);
}

.author-badge-links a:hover {
  color: var(--accent-light);
}

.start-btn {
  background: var(--gradient-hero);
  color: #fff;
  border: none;
  padding: 16px 40px;
  border-radius: 14px;
  font-family: 'Outfit', sans-serif;
  font-size: 1.1rem;
  font-weight: 700;
  cursor: pointer;
  transition: var(--transition);
  box-shadow: 0 8px 32px rgba(251, 191, 36, 0.4);
  margin-bottom: 40px;
}

.start-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 40px rgba(251, 191, 36, 0.5);
}

/* Series checklist */
.series-checklist {
  background: var(--bg-glass);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: var(--radius);
  padding: 24px;
  max-width: 460px;
  width: 100%;
  margin-bottom: 32px;
}

.series-checklist h3 {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: var(--text-muted);
  margin-bottom: 16px;
}

.series-checklist h3 span {
  color: var(--accent-primary);
}

.checklist-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
}

.checklist-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  color: var(--text-muted);
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid rgba(255, 255, 255, 0.04);
}

.checklist-item.completed {
  color: var(--accent-green);
  background: rgba(16, 185, 129, 0.08);
  border-color: rgba(16, 185, 129, 0.15);
}

.checklist-item.current {
  color: var(--accent-primary);
  background: rgba(251, 191, 36, 0.08);
  border-color: rgba(251, 191, 36, 0.2);
  box-shadow: 0 0 12px rgba(251, 191, 36, 0.15);
}

.check-box {
  width: 22px;
  height: 22px;
  border-radius: 6px;
  border: 2px solid rgba(255, 255, 255, 0.15);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  flex-shrink: 0;
}

.checklist-item.completed .check-box {
  background: var(--accent-green);
  border-color: var(--accent-green);
  color: #fff;
}

.checklist-item.current .check-box {
  background: var(--accent-primary);
  border-color: var(--accent-primary);
  color: #fff;
}

.cover-characters {
  margin-top: 24px;
}

.cover-characters img {
  width: min(480px, 90%);
  border-radius: 16px;
  box-shadow: none;
}

.cover-footer {
  margin-top: 40px;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.cover-footer p {
  margin-bottom: 4px;
}

/* ===== PROGRESS BAR ===== */
.progress-bar {
  position: fixed;
  top: 0;
  left: 300px;
  right: 0;
  height: 3px;
  background: rgba(255, 255, 255, 0.05);
  z-index: 150;
  transition: left var(--transition);
}

.progress-fill {
  height: 100%;
  background: var(--gradient-hero);
  width: 0%;
  transition: width 0.2s ease;
}

/* ===== SCROLL PROGRESS (within chapter) ===== */
#scrollProgress {
  position: fixed;
  top: 3px;
  left: 300px;
  right: 0;
  height: 2px;
  background: var(--accent-primary);
  z-index: 151;
  transition: width 0.1s linear;
  width: 0%;
}

@media (max-width: 900px) {
  #scrollProgress {
    left: 0;
  }
}


/* ===== SIDEBAR FOOTER ===== */
.sidebar-footer {
  padding: 16px 20px;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  text-align: center;
  font-size: 0.78rem;
  color: var(--text-muted);
}

.sidebar-footer a {
  color: var(--accent-primary);
  text-decoration: none;
  display: block;
  margin-top: 4px;
}

/* ===== SCROLL REVEAL ===== */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ===== ANIMATED DEMO CONTAINERS ===== */
.demo-container {
  margin: 32px 0;
  padding: 32px;
  border-radius: var(--radius);
  background: rgba(251, 191, 36, 0.04);
  border: 1px solid rgba(251, 191, 36, 0.15);
  overflow: hidden;
}

.demo-container h4 {
  font-size: 0.85rem;
  color: var(--accent-primary);
  text-transform: uppercase;
  letter-spacing: 2px;
  margin-bottom: 20px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.demo-label {
  font-size: 0.72rem;
  color: var(--text-muted);
  text-align: center;
  margin-top: 12px;
}

/* ===== MULTI-LANGUAGE CODE TABS ===== */
.code-tabs {
  margin: 24px 0;
  border-radius: var(--radius);
  background: #0d1117;
  border: 1px solid rgba(255, 255, 255, 0.08);
  overflow: hidden;
}

.code-tabs-header {
  display: flex;
  background: rgba(255, 255, 255, 0.04);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
  overflow-x: auto;
}

.code-tab-btn {
  padding: 10px 16px;
  background: none;
  border: none;
  color: var(--text-muted);
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  white-space: nowrap;
  border-bottom: 2px solid transparent;
  text-transform: uppercase;
}

.code-tab-btn:hover {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.03);
}

.code-tab-btn.active {
  color: var(--accent-primary);
  border-bottom-color: var(--accent-primary);
  background: rgba(251, 191, 36, 0.08);
}

.code-tab-content {
  display: none;
}

.code-tab-content.active {
  display: block;
}

.code-tab-content pre {
  padding: 20px;
  overflow-x: auto;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.88rem;
  line-height: 1.7;
  color: #c9d1d9;
}

/* ===== RESPONSIVE ===== */
@media (max-width: 900px) {
  .sidebar {
    transform: translateX(-300px);
  }

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

  .nav-toggle {
    display: flex;
  }

  .main-content {
    margin-left: 0;
  }

  .progress-bar {
    left: 0;
  }

  .chapter-hero-overlay {
    padding: 24px 20px 28px;
  }

  .chapter-hero-overlay h1 {
    font-size: 1.8rem;
  }

  .chapter-body {
    padding: 32px 16px 60px;
  }

  .cover-page h1 {
    font-size: 2.4rem;
  }

  .chapter-nav {
    flex-direction: column;
    gap: 12px;
  }

  .chapter-nav-btn {
    width: 100%;
    justify-content: center;
  }

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

  .compare-table {
    font-size: 0.85rem;
  }

  .compare-table th,
  .compare-table td {
    padding: 10px 12px;
  }

  .dialogue {
    flex-direction: column;
    gap: 12px;
  }

  .code-tabs-header {
    flex-wrap: nowrap;
    -webkit-overflow-scrolling: touch;
  }
}

@media (max-width: 500px) {
  .cover-page h1 {
    font-size: 2rem;
  }

  .chapter-hero-overlay h1 {
    font-size: 1.5rem;
  }

  .chapter-body h2 {
    font-size: 1.4rem;
  }

  .chapter-body { padding: 24px 14px 50px; }
  .chapter-body h3 { font-size: 1.1rem; }
  .chapter-body p, .chapter-body li { font-size: 0.95rem; line-height: 1.65; }
  .chapter-hero-overlay { padding: 18px 14px 22px; }
  .dialogue { padding: 14px 12px; gap: 10px; }
  .dialogue-avatar { width: 38px; height: 38px; font-size: 0.95rem; }
}

/* ===== Narrow-phone safety net (tables / code / mermaid scroll) ===== */
@media (max-width: 720px) {
  .chapter-body table {
    display: block; overflow-x: auto; -webkit-overflow-scrolling: touch;
    white-space: nowrap; max-width: 100%;
  }
  .chapter-body pre,
  .chapter-body code,
  .chapter-body .mermaid {
    max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch;
  }
  .chapter-body pre { font-size: 0.78rem; }
  .chapter-body img { max-width: 100%; height: auto; }
  .chapter-body iframe { max-width: 100%; }
}

/* ===== DEDICATION PAGE ===== */
.dedication-page {
  min-height: 80vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 60px 30px;
}

.dedication-card {
  max-width: 520px;
  text-align: center;
  padding: 48px 36px;
  background: var(--bg-glass);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: 24px;
}

.dedication-card .ded-icon {
  font-size: 2.5rem;
  margin-bottom: 20px;
}

.dedication-card .ded-text {
  font-size: 1.15rem;
  line-height: 1.9;
  color: var(--text-secondary);
  font-style: italic;
}

.dedication-card .ded-text strong {
  color: var(--accent-primary);
}

/* ===== PREFACE ===== */
.preface-page {
  max-width: 800px;
  margin: 0 auto;
  padding: 60px 32px 80px;
}

.preface-page h1 {
  font-size: 2.2rem;
  font-weight: 800;
  margin-bottom: 24px;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.preface-page p {
  color: var(--text-secondary);
  font-size: 1.02rem;
  margin-bottom: 16px;
  line-height: 1.8;
}

.preface-page h3 {
  font-size: 1.2rem;
  color: var(--accent-light);
  margin: 32px 0 12px;
}

.preface-page ul {
  padding-left: 24px;
  color: var(--text-secondary);
}

.preface-page li {
  margin-bottom: 8px;
  font-size: 0.95rem;
}