/* ============================================
   FONT FACES
   ============================================ */
@font-face {
  font-family: 'Inter';
  src: url('../fonts/Inter/Inter-Regular.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: 'Inter';
  src: url('../fonts/Inter/Inter-Bold.woff2') format('woff2');
  font-weight: 700;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: 'Merriweather';
  src: url('../fonts/Merriweather/Merriweather-Regular.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: 'Merriweather';
  src: url('../fonts/Merriweather/Merriweather-Italic.woff2') format('woff2');
  font-weight: 400;
  font-style: italic;
  font-display: swap;
}
@font-face {
  font-family: 'JetBrains Mono';
  src: url('../fonts/JetBrainsMono/JetBrainsMono-Regular.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}

/* ============================================
   CSS VARIABLES (Light & Dark)
   ============================================ */
:root {
  --bg: #faf8f5;
  --text: #2d2d2d;
  --text-light: #666;
  --heading: #1a1a2e;
  --accent: #16213e;
  --gold: #d4a574;
  --gold-light: #e8d5b0;
  --sidebar-bg: #1a1a2e;
  --sidebar-text: #aaa;
  --sidebar-hover: #d4a574;
  --card-bg: #fff;
  --border: #e0d8cc;
  --blockquote-bg: #f0f4f8;
  --code-bg: #f0f0f0;
  --shadow: 0 2px 15px rgba(0,0,0,0.05);
  --font-body: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-heading: 'Merriweather', Georgia, 'Times New Roman', serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;
}

body.dark {
  --bg: #1a1a2e;
  --text: #ccc;
  --text-light: #999;
  --heading: #e0d8cc;
  --accent: #d4a574;
  --card-bg: #252540;
  --border: #333;
  --blockquote-bg: #252540;
  --code-bg: #333;
  --shadow: 0 2px 15px rgba(0,0,0,0.3);
}

/* ============================================
   RESET & BASE
   ============================================ */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  display: flex;
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
}

code, pre {
  font-family: var(--font-mono);
}

/* ============================================
   SIDEBAR
   ============================================ */
.sidebar {
  width: 280px;
  background: var(--sidebar-bg);
  color: var(--sidebar-text);
  padding: 30px 20px;
  position: fixed;
  top: 0; left: 0;
  height: 100vh;
  overflow-y: auto;
  z-index: 100;
  transition: transform 0.3s ease;
}
.sidebar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 25px;
}
.sidebar h2 {
  color: var(--gold);
  font-size: 1.1em;
  text-align: center;
  flex: 1;
  font-family: var(--font-heading);
}
.sidebar-close {
  display: none;
  background: none;
  border: none;
  color: #aaa;
  font-size: 1.5em;
  cursor: pointer;
}
.sidebar ul { list-style: none; padding: 0; }
.sidebar ul li { margin-bottom: 4px; }
.sidebar ul li a {
  color: var(--sidebar-text);
  text-decoration: none;
  font-size: 0.85em;
  display: block;
  padding: 7px 12px;
  border-radius: 4px;
  transition: all 0.2s;
  border-left: 2px solid transparent;
}
.sidebar ul li a:hover,
.sidebar ul li a.active {
  color: var(--gold);
  background: rgba(255,255,255,0.05);
  border-left-color: var(--gold);
}
.sidebar .part-title {
  color: var(--gold-light);
  font-weight: bold;
  margin-top: 22px;
  margin-bottom: 8px;
  font-size: 0.8em;
  letter-spacing: 1px;
  opacity: 0.8;
  text-transform: uppercase;
}

/* ============================================
   SIDEBAR OVERLAY (mobile)
   ============================================ */
.sidebar-overlay {
  display: none;
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  background: rgba(0,0,0,0.5);
  z-index: 99;
}

/* ============================================
   TOP BAR (mobile)
   ============================================ */
.topbar {
  display: none;
  position: sticky;
  top: 0;
  background: var(--bg);
  padding: 12px 15px;
  border-bottom: 1px solid var(--border);
  z-index: 50;
  align-items: center;
  justify-content: space-between;
}
.hamburger {
  background: none;
  border: none;
  font-size: 1.5em;
  cursor: pointer;
  color: var(--text);
}
.topbar-title {
  font-weight: bold;
  color: var(--heading);
}
.theme-toggle {
  background: none;
  border: none;
  font-size: 1.3em;
  cursor: pointer;
  color: var(--text);
}

/* ============================================
   MAIN CONTENT
   ============================================ */
.main-content {
  margin-left: 280px;
  padding: 40px 60px;
  max-width: 900px;
  width: 100%;
  min-height: 100vh;
}

/* ============================================
   BOOK COVER
   ============================================ */
.book-cover {
  text-align: center;
  padding: 80px 20px 60px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 50px;
}
.cover-content { max-width: 650px; margin: 0 auto; }
.cover-series {
  font-size: 0.85em;
  color: var(--text-light);
  letter-spacing: 3px;
  margin-bottom: 20px;
  text-transform: uppercase;
}
.book-cover h1 {
  font-size: 3em;
  font-weight: 700;
  color: var(--heading);
  margin-bottom: 10px;
  letter-spacing: 1px;
  font-family: var(--font-heading);
}
.cover-subtitle {
  font-size: 1.15em;
  color: var(--text-light);
  margin-bottom: 20px;
}
.cover-divider {
  width: 60px; height: 2px;
  background: var(--gold);
  margin: 20px auto;
}
.cover-author {
  font-size: 1.1em;
  color: var(--heading);
  font-weight: 700;
  margin-bottom: 15px;
}
.cover-tagline {
  font-size: 1.2em;
  color: var(--gold);
  font-style: italic;
  margin-bottom: 20px;
}
.cover-description {
  font-size: 0.95em;
  color: var(--text-light);
  margin-bottom: 30px;
  line-height: 1.8;
}
.cover-links { margin-bottom: 25px; }
.cover-btn {
  display: inline-block;
  padding: 12px 28px;
  border-radius: 50px;
  margin: 0 8px;
  text-decoration: none;
  font-weight: bold;
  transition: all 0.3s;
  font-size: 0.95em;
}
.cover-btn.outline {
  border: 2px solid var(--accent);
  color: var(--accent);
}
.cover-btn.outline:hover { background: var(--accent); color: #fff; }
.cover-btn.filled {
  background: var(--accent);
  color: #fff;
  border: 2px solid var(--accent);
}
.cover-btn.filled:hover { opacity: 0.85; }
.cover-year {
  font-size: 0.85em;
  color: var(--text-light);
}

/* ============================================
   CHAPTER CONTENT
   ============================================ */
.chapter-content {
  padding: 20px 0;
}
.chapter-content h2 {
  font-size: 1.8em;
  color: var(--heading);
  margin: 50px 0 20px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--gold);
  font-family: var(--font-heading);
}
.chapter-content h3 {
  font-size: 1.2em;
  color: var(--accent);
  margin: 30px 0 12px;
  font-family: var(--font-heading);
}
.chapter-content p {
  margin-bottom: 18px;
  text-align: left;
}
.chapter-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 25px 0;
  font-size: 0.9em;
}
.chapter-content th {
  background: var(--sidebar-bg);
  color: #fff;
  padding: 10px 12px;
  border: 1px solid var(--border);
  text-align: left;
}
.chapter-content td {
  padding: 10px 12px;
  border: 1px solid var(--border);
}
.chapter-content tr:nth-child(even) td { background: rgba(0,0,0,0.02); }
.chapter-content blockquote {
  background: var(--blockquote-bg);
  border-left: 4px solid var(--accent);
  padding: 18px 22px;
  margin: 25px 0;
  font-style: italic;
  border-radius: 4px;
}
.chapter-content code {
  background: var(--code-bg);
  padding: 2px 7px;
  border-radius: 3px;
  font-size: 0.9em;
  font-family: var(--font-mono);
}
.chapter-content ul, .chapter-content ol {
  margin: 15px 0 20px 20px;
}
.chapter-content li { margin-bottom: 8px; }

/* ============================================
   FOOTER
   ============================================ */
.book-footer {
  text-align: center;
  padding: 40px 20px;
  margin-top: 60px;
  border-top: 1px solid var(--border);
  color: var(--text-light);
  font-size: 0.85em;
}
.book-footer a { color: var(--gold); text-decoration: none; }

/* ============================================
   RESPONSIVE
   ============================================ */
@media (max-width: 768px) {
  .sidebar {
    transform: translateX(-100%);
  }
  .sidebar.open {
    transform: translateX(0);
  }
  .sidebar-close { display: block; }
  .sidebar-overlay.active { display: block; }
  .main-content {
    margin-left: 0;
    padding: 15px;
  }
  .topbar { display: flex; }
  .book-cover { padding: 50px 15px 40px; }
  .book-cover h1 { font-size: 2em; }
  .cover-btn { display: block; margin: 10px auto; max-width: 250px; }
}

/* ============================================
   CHAPTER NAVIGATION
   ============================================ */
.chapter-nav {
  display: none;
  justify-content: space-between;
  align-items: center;
  padding: 25px 0;
  margin-top: 50px;
  border-top: 1px solid var(--border);
  gap: 15px;
}

.nav-btn {
  display: inline-block;
  padding: 14px 24px;
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  text-decoration: none;
  transition: all 0.3s;
  cursor: pointer;
  font-family: var(--font-body);
  font-size: 0.9em;
  background: var(--card-bg);
  max-width: 45%;
  text-align: center;
}

.nav-btn:hover {
  border-color: var(--gold);
  color: var(--gold);
  background: rgba(212, 165, 116, 0.05);
}

.nav-btn:active {
  transform: scale(0.98);
}

.nav-btn.hidden {
  visibility: hidden;
}

/* Chapter title in top bar */
.chapter-title-top {
  font-size: 0.9em;
  color: var(--text-light);
  max-width: 300px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* Progress indicator */
.progress-indicator {
  text-align: center;
  color: var(--text-light);
  font-size: 0.85em;
  margin-top: 0;
}

/* ============================================
   ICDM BOOK — ADDITIONAL STYLES
   ============================================ */

/* Chapter header */
.chapter-header {
  margin-bottom: 40px;
  text-align: center;
}
.chapter-section {
  font-size: 0.85em;
  color: var(--text-light);
  letter-spacing: 2px;
  text-transform: uppercase;
  margin-bottom: 10px;
}
.chapter-title {
  font-size: 2.2em;
  font-weight: 700;
  color: var(--heading);
  margin-bottom: 10px;
  line-height: 1.5;
  font-family: var(--font-heading);
}
.chapter-subtitle {
  font-size: 1.1em;
  color: var(--text-light);
  font-style: italic;
}

/* Scene box */
.scene {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 25px 30px;
  margin: 30px 0;
  box-shadow: var(--shadow);
}

/* Insight box */
.insight {
  background: var(--blockquote-bg);
  border-left: 4px solid var(--gold);
  padding: 20px 25px;
  margin: 30px 0;
  border-radius: 4px;
}

/* Core claim */
.core-claim {
  background: var(--sidebar-bg);
  color: #fff;
  padding: 25px 30px;
  margin: 30px 0;
  border-radius: 8px;
}
.core-claim h2,
.core-claim h3 {
  color: var(--gold) !important;
  border-bottom: none !important;
  font-family: var(--font-heading);
}
.core-claim p,
.core-claim li {
  color: #ddd;
}
.core-claim code {
  background: rgba(255,255,255,0.15);
  color: #eee;
}

/* Question highlight */
.question {
  font-size: 1.15em;
  font-weight: 700;
  color: var(--accent);
  text-align: center;
  margin: 30px 0;
  padding: 15px;
  background: rgba(212, 165, 116, 0.1);
  border-radius: 6px;
}

/* Dialogue */
.dialogue {
  font-style: italic;
  color: var(--accent);
  font-weight: 700;
}

/* Code block */
.code-block {
  margin: 20px 0;
  direction: ltr;
  text-align: left;
}
.code-block pre {
  background: #1e1e2e;
  color: #cdd6f4;
  padding: 18px 22px;
  border-radius: 8px;
  overflow-x: auto;
  font-size: 0.85em;
  line-height: 1.7;
  font-family: var(--font-mono);
}
.code-block code {
  background: none;
  padding: 0;
  color: inherit;
}

/* Preview box */
.preview {
  background: rgba(212, 165, 116, 0.08);
  border: 1px dashed var(--gold);
  border-radius: 8px;
  padding: 20px 25px;
  margin: 40px 0 20px;
}
.preview h2 {
  color: var(--gold);
  border-bottom: none;
  margin-top: 0;
}

/* Deep dive */
.deep-dive {
  margin: 30px 0;
}

/* Thesis / blockquote special */
.thesis blockquote {
  font-size: 1.1em;
  font-weight: 600;
}

/* Comparison layout */
.comparison {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin: 25px 0;
}
.comparison-left,
.comparison-right {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px;
}
.comparison h3 {
  margin-top: 0;
}

/* Concept box */
.concept-box {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px 25px;
  margin: 20px 0;
}
.concept-box h3 {
  color: var(--gold);
  margin-top: 0;
}

/* Principle box */
.principle-box {
  background: var(--blockquote-bg);
  border: 2px solid var(--accent);
  border-radius: 8px;
  padding: 25px 30px;
  margin: 25px 0;
  text-align: center;
}
.principle-statement {
  font-size: 1.15em;
  font-weight: 700;
  color: var(--heading);
}

/* Theorem box */
.theorem-box {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-right: 4px solid var(--gold);
  padding: 20px 25px;
  margin: 20px 0;
  border-radius: 4px;
}
.theorem-statement {
  font-weight: 700;
  color: var(--accent);
}

/* Level boxes */
.level-box {
  padding: 20px 25px;
  margin: 20px 0;
  border-radius: 8px;
}
.level-box.level-1 { background: #fde8e8; border: 1px solid #e53e3e; }
.level-box.level-2 { background: #fef3c7; border: 1px solid #d69e2e; }
.level-box.level-3 { background: #c6f6d5; border: 1px solid #38a169; }
.level-box.level-4 { background: #bee3f8; border: 1px solid #3182ce; }
.level-title {
  font-weight: 700;
  margin-bottom: 8px;
}

/* Question box */
.question-box {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 18px 22px;
  margin: 15px 0;
}

/* Answer box */
.answer-box {
  padding: 15px 22px;
  margin: 10px 0 20px;
}

/* Formula */
.formula {
  text-align: center;
  margin: 30px 0;
}
.formula-result {
  font-size: 1.2em;
  font-weight: 700;
  color: var(--heading);
  padding: 15px;
  background: var(--blockquote-bg);
  border-radius: 8px;
  display: inline-block;
}

/* Section range */
.section-range {
  font-size: 0.85em;
  color: var(--text-light);
  margin-bottom: 10px;
}

/* Timeline */
.timeline {
  margin: 25px 0;
}
.timeline-item {
  padding: 12px 20px;
  margin-bottom: 10px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 0.9em;
}
.timeline-item strong {
  color: var(--accent);
}

/* Table centered text */
.chapter-content td {
  vertical-align: middle;
}

/* Navigation visibility */
.chapter-nav {
  display: flex;
}

/* Loading and error states */
.loading {
  text-align: center;
  padding: 60px 20px;
  color: var(--text-light);
  font-size: 1.1em;
}
.error {
  text-align: center;
  padding: 60px 20px;
  color: #e53e3e;
}
.error-detail {
  font-size: 0.85em;
  color: var(--text-light);
  margin-top: 10px;
}

/* ============================================
   RESPONSIVE — ADDITIONAL
   ============================================ */
@media (max-width: 768px) {
  .comparison {
    grid-template-columns: 1fr;
  }
  .chapter-title {
    font-size: 1.6em;
  }
  .core-claim {
    padding: 18px 20px;
  }
  .chapter-nav {
    flex-direction: column;
    gap: 10px;
  }
  .nav-btn {
    max-width: 100%;
    text-align: center;
  }
}