/* ==========================================================================
   HEARD IN DATA SCIENCE INTERVIEWS (2ND EDITION) - OFFICIAL WEBSITE STYLES
   Design System: Midnight Obsidian, Electric Cyan (#00e5ff), Warm Amber Gold (#ffc107)
   ========================================================================== */

:root {
  /* Color Palette */
  --bg-primary: #0b0f19;
  --bg-secondary: #0f172a;
  --bg-tertiary: #1e293b;
  --bg-card: rgba(30, 41, 59, 0.7);
  --bg-card-hover: rgba(51, 65, 85, 0.8);
  --bg-glass: rgba(15, 23, 42, 0.75);
  
  --border-subtle: #334155;
  --border-focus: #00e5ff;
  --border-gold: rgba(255, 193, 7, 0.35);
  
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-dark: #0f172a;
  
  --accent-cyan: #00e5ff;
  --accent-cyan-light: #38bdf8;
  --accent-cyan-glow: rgba(0, 229, 255, 0.25);
  --accent-gold: #ffc107;
  --accent-gold-light: #ffe082;
  --accent-gold-glow: rgba(255, 193, 7, 0.25);
  
  --status-confirmed: #10b981;
  --status-pending: #f59e0b;
  --status-fixed: #3b82f6;
  
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-heading: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', Consolas, Monaco, monospace;
  
  /* Layout & Spacing */
  --max-width: 1200px;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 9999px;
  
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.5);
  --shadow-cyan: 0 0 30px rgba(0, 229, 255, 0.2);
  --shadow-gold: 0 0 30px rgba(255, 193, 7, 0.2);
  
  --transition-fast: 0.15s ease;
  --transition-normal: 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
  background-color: var(--bg-primary);
  color: var(--text-primary);
}

body {
  font-family: var(--font-sans);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  background: radial-gradient(circle at 50% 0%, #172554 0%, #0b0f19 70%);
  min-height: 100vh;
  overflow-x: hidden;
}

a {
  color: var(--accent-cyan-light);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-cyan);
  text-decoration: underline;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

/* Container */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* ==========================================================================
   NAVIGATION BAR
   ========================================================================== */
.navbar {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-subtle);
  transition: all var(--transition-normal);
}

.nav-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 1.15rem;
  color: var(--text-primary);
  text-decoration: none;
}

.nav-brand:hover {
  text-decoration: none;
}

.brand-badge {
  background: linear-gradient(135deg, #0284c7, #0369a1);
  color: #e0f2fe;
  font-size: 0.7rem;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: var(--radius-pill);
  letter-spacing: 0.5px;
  border: 1px solid rgba(56, 189, 248, 0.4);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 1.75rem;
  list-style: none;
}

.nav-link {
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  transition: color var(--transition-fast);
}

.nav-link:hover, .nav-link.active {
  color: var(--accent-cyan);
  text-decoration: none;
}

.nav-cta {
  background: linear-gradient(135deg, #ffc107, #f59e0b);
  color: var(--text-dark);
  font-weight: 700;
  font-size: 0.9rem;
  padding: 8px 18px;
  border-radius: var(--radius-pill);
  box-shadow: 0 4px 12px rgba(245, 158, 11, 0.3);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  text-decoration: none;
}

.nav-cta:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(245, 158, 11, 0.45);
  color: var(--text-dark);
  text-decoration: none;
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  cursor: pointer;
}

/* ==========================================================================
   HERO SECTION
   ========================================================================== */
.hero {
  padding: 4rem 0 5rem;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: 10%;
  left: 50%;
  transform: translateX(-50%);
  width: 800px;
  height: 400px;
  background: radial-gradient(ellipse, rgba(0, 229, 255, 0.12) 0%, rgba(255, 193, 7, 0.05) 50%, transparent 70%);
  filter: blur(60px);
  pointer-events: none;
  z-index: 0;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 3.5rem;
  align-items: center;
  position: relative;
  z-index: 1;
}

.hero-badge-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(15, 23, 42, 0.9);
  border: 1.5px solid var(--accent-gold);
  color: var(--accent-gold);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.8px;
  text-transform: uppercase;
  padding: 6px 16px;
  border-radius: var(--radius-pill);
  margin-bottom: 1.5rem;
  box-shadow: 0 0 16px rgba(255, 193, 7, 0.2);
}

.audience-callout {
  color: var(--accent-cyan);
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  margin-bottom: 0.75rem;
}

.hero-title {
  font-family: var(--font-heading);
  font-size: clamp(2.4rem, 5vw, 3.6rem);
  font-weight: 900;
  line-height: 1.15;
  letter-spacing: -0.02em;
  margin-bottom: 0.75rem;
  color: #ffffff;
}

.hero-title .title-accent {
  background: linear-gradient(135deg, #00e5ff 0%, #38bdf8 50%, #818cf8 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  display: block;
}

.hero-subtitle {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--accent-gold);
  margin-bottom: 0.75rem;
  line-height: 1.4;
}

.hero-tagline {
  font-family: 'Times New Roman', Times, serif;
  font-style: italic;
  font-size: 1.15rem;
  color: var(--accent-cyan-light);
  margin-bottom: 1.5rem;
}

.hero-desc {
  color: var(--text-secondary);
  font-size: 1.05rem;
  margin-bottom: 2rem;
  line-height: 1.7;
}

.hero-ctas {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  margin-bottom: 2.5rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1rem;
  padding: 12px 26px;
  border-radius: var(--radius-md);
  transition: all var(--transition-normal);
  cursor: pointer;
  border: none;
  text-decoration: none;
}

.btn-primary {
  background: linear-gradient(135deg, #ffc107 0%, #f59e0b 100%);
  color: #020617;
  box-shadow: 0 6px 20px rgba(245, 158, 11, 0.35);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 10px 28px rgba(245, 158, 11, 0.5);
  color: #020617;
  text-decoration: none;
}

.btn-secondary {
  background: rgba(30, 41, 59, 0.8);
  color: var(--text-primary);
  border: 1px solid var(--border-subtle);
  backdrop-filter: blur(8px);
}

.btn-secondary:hover {
  background: rgba(51, 65, 85, 0.9);
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
  text-decoration: none;
  transform: translateY(-2px);
}

.btn-outline {
  background: transparent;
  color: var(--text-secondary);
  border: 1px solid var(--border-subtle);
}

.btn-outline:hover {
  border-color: var(--text-primary);
  color: var(--text-primary);
  text-decoration: none;
}

.hero-meta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
  font-size: 0.88rem;
  color: var(--text-muted);
  border-top: 1px solid var(--border-subtle);
  padding-top: 1.25rem;
}

.hero-meta-item {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.hero-meta-item strong {
  color: var(--text-secondary);
}

/* Hero Book Mockup */
.hero-book-wrapper {
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}

.book-card-mockup {
  position: relative;
  border-radius: var(--radius-lg);
  perspective: 1200px;
  transition: transform var(--transition-normal);
}

.book-card-mockup:hover {
  transform: translateY(-8px) rotateY(-4deg);
}

.book-cover-img {
  width: 100%;
  max-width: 380px;
  border-radius: var(--radius-md);
  box-shadow: -12px 18px 40px rgba(0, 0, 0, 0.8),
              0 0 35px rgba(0, 229, 255, 0.2);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.book-glow {
  position: absolute;
  inset: -20px;
  background: radial-gradient(circle at 60% 60%, rgba(0, 229, 255, 0.25), rgba(255, 193, 7, 0.1), transparent 70%);
  filter: blur(30px);
  z-index: -1;
  pointer-events: none;
}

/* ==========================================================================
   METRICS / STATS STRIP
   ========================================================================== */
.stats-strip {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  border-bottom: 1px solid var(--border-subtle);
  padding: 2.5rem 0;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 2rem;
  text-align: center;
}

.stat-item {
  padding: 0.5rem;
}

.stat-number {
  font-family: var(--font-heading);
  font-size: 2.5rem;
  font-weight: 800;
  color: var(--accent-cyan);
  line-height: 1;
  margin-bottom: 0.35rem;
}

.stat-number.gold {
  color: var(--accent-gold);
}

.stat-label {
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.stat-desc {
  color: var(--text-muted);
  font-size: 0.8rem;
  margin-top: 0.25rem;
}

/* ==========================================================================
   SECTION HEADINGS & LAYOUT
   ========================================================================== */
.section {
  padding: 5rem 0;
  position: relative;
}

.section-alt {
  background: rgba(15, 23, 42, 0.5);
}

.section-header {
  text-align: center;
  max-width: 760px;
  margin: 0 auto 3.5rem;
}

.section-tag {
  color: var(--accent-cyan);
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  margin-bottom: 0.5rem;
  display: inline-block;
}

.section-title {
  font-family: var(--font-heading);
  font-size: clamp(2rem, 3.5vw, 2.75rem);
  font-weight: 800;
  color: #ffffff;
  line-height: 1.2;
  margin-bottom: 1rem;
}

.section-subtitle {
  color: var(--text-secondary);
  font-size: 1.1rem;
  line-height: 1.6;
}

/* ==========================================================================
   FEATURE CARDS (WHAT'S NEW / WHY THIS BOOK)
   ========================================================================== */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 1.75rem;
}

.feature-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 2rem;
  transition: all var(--transition-normal);
  position: relative;
  overflow: hidden;
  backdrop-filter: blur(10px);
}

.feature-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, transparent, var(--accent-cyan), transparent);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.feature-card:hover {
  transform: translateY(-4px);
  border-color: rgba(0, 229, 255, 0.4);
  background: var(--bg-card-hover);
  box-shadow: var(--shadow-cyan);
}

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

.feature-icon-wrapper {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-sm);
  background: rgba(0, 229, 255, 0.1);
  border: 1px solid rgba(0, 229, 255, 0.3);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  color: var(--accent-cyan);
  margin-bottom: 1.25rem;
}

.feature-card.gold-theme .feature-icon-wrapper {
  background: rgba(255, 193, 7, 0.1);
  border-color: rgba(255, 193, 7, 0.3);
  color: var(--accent-gold);
}

.feature-card.gold-theme:hover {
  border-color: rgba(255, 193, 7, 0.4);
  box-shadow: var(--shadow-gold);
}

.feature-card.gold-theme:hover::before {
  background: linear-gradient(90deg, transparent, var(--accent-gold), transparent);
}

.feature-title {
  font-family: var(--font-heading);
  font-size: 1.25rem;
  font-weight: 700;
  color: #ffffff;
  margin-bottom: 0.75rem;
}

.feature-desc {
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.6;
}

.feature-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 1.25rem;
}

.tag-pill {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 3px 9px;
  border-radius: var(--radius-pill);
  background: rgba(255, 255, 255, 0.06);
  color: var(--text-secondary);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

/* ==========================================================================
   TABLE OF CONTENTS / SYLLABUS ACCORDION
   ========================================================================== */
.toc-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.toc-count-badge {
  background: rgba(0, 229, 255, 0.1);
  border: 1px solid rgba(0, 229, 255, 0.3);
  color: var(--accent-cyan);
  font-size: 0.9rem;
  font-weight: 700;
  padding: 6px 14px;
  border-radius: var(--radius-pill);
}

.toc-btn-group {
  display: flex;
  gap: 0.5rem;
}

.toc-accordion {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.toc-item {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.toc-item:hover {
  border-color: #475569;
}

.toc-header {
  padding: 1.25rem 1.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  user-select: none;
  background: transparent;
  transition: background var(--transition-fast);
}

.toc-header:hover {
  background: rgba(255, 255, 255, 0.03);
}

.toc-title-group {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.toc-chapter-num {
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 0.85rem;
  color: var(--accent-cyan);
  background: rgba(0, 229, 255, 0.12);
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  letter-spacing: 0.5px;
}

.toc-chapter-name {
  font-family: var(--font-heading);
  font-size: 1.15rem;
  font-weight: 700;
  color: #ffffff;
}

.toc-meta-group {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.toc-q-badge {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--accent-gold);
  background: rgba(255, 193, 7, 0.1);
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  border: 1px solid rgba(255, 193, 7, 0.25);
}

.toc-toggle-icon {
  font-size: 1.1rem;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
}

.toc-item.open .toc-toggle-icon {
  transform: rotate(180deg);
  color: var(--accent-cyan);
}

.toc-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease-out, padding 0.35s ease;
  padding: 0 1.75rem;
  background: rgba(15, 23, 42, 0.5);
  border-top: 1px solid transparent;
}

.toc-item.open .toc-body {
  max-height: 800px;
  padding: 1.25rem 1.75rem 1.75rem;
  border-top-color: var(--border-subtle);
}

.toc-topic-list {
  list-style: none;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 0.75rem;
}

.toc-topic-item {
  display: flex;
  align-items: flex-start;
  gap: 0.6rem;
  font-size: 0.92rem;
  color: var(--text-secondary);
  line-height: 1.45;
}

.toc-topic-item::before {
  content: '✦';
  color: var(--accent-cyan);
  font-size: 0.75rem;
  margin-top: 2px;
}

/* ==========================================================================
   SAMPLE QUESTION SHOWCASE
   ========================================================================== */
.sample-showcase {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
}

.sample-tabs {
  display: flex;
  background: #020617;
  border-bottom: 1px solid var(--border-subtle);
  overflow-x: auto;
}

.sample-tab {
  padding: 1rem 1.5rem;
  background: transparent;
  border: none;
  color: var(--text-muted);
  font-family: var(--font-heading);
  font-size: 0.92rem;
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
  transition: all var(--transition-fast);
  border-bottom: 2px solid transparent;
}

.sample-tab:hover {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.02);
}

.sample-tab.active {
  color: var(--accent-cyan);
  border-bottom-color: var(--accent-cyan);
  background: rgba(0, 229, 255, 0.05);
}

.sample-content {
  display: none;
  padding: 2.25rem;
}

.sample-content.active {
  display: block;
}

.sample-header {
  margin-bottom: 1.5rem;
}

.sample-meta {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.75rem;
}

.sample-tag {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  background: rgba(0, 229, 255, 0.15);
  color: var(--accent-cyan);
}

.sample-q-num {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.sample-question-title {
  font-family: var(--font-heading);
  font-size: 1.35rem;
  font-weight: 700;
  color: #ffffff;
  line-height: 1.4;
}

.sample-answer-box {
  background: #020617;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 1.75rem;
}

.answer-lead {
  font-weight: 600;
  color: var(--accent-gold);
  margin-bottom: 1rem;
  font-size: 1.05rem;
}

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

.answer-body p {
  margin-bottom: 1rem;
}

.answer-body ul, .answer-body ol {
  margin-left: 1.5rem;
  margin-bottom: 1rem;
}

.code-block {
  background: #090d16;
  border: 1px solid #1e293b;
  border-radius: var(--radius-sm);
  padding: 1.25rem;
  margin: 1rem 0;
  font-family: var(--font-mono);
  font-size: 0.88rem;
  overflow-x: auto;
  color: #e2e8f0;
  line-height: 1.5;
}

.code-keyword { color: #38bdf8; font-weight: bold; }
.code-func { color: #facc15; }
.code-comment { color: #64748b; font-style: italic; }
.code-str { color: #4ade80; }
.code-num { color: #f472b6; }

.math-formula {
  background: rgba(30, 41, 59, 0.6);
  border-left: 3px solid var(--accent-cyan);
  padding: 0.85rem 1.25rem;
  margin: 1rem 0;
  font-family: var(--font-mono);
  font-size: 0.92rem;
  color: #f1f5f9;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

/* ==========================================================================
   ABOUT THE AUTHOR
   ========================================================================== */
.author-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 3rem;
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 3rem;
  align-items: center;
  backdrop-filter: blur(10px);
}

.author-photo-wrapper {
  text-align: center;
}

.author-photo {
  width: 180px;
  height: 180px;
  border-radius: 50%;
  border: 3px solid var(--accent-cyan);
  box-shadow: 0 0 25px rgba(0, 229, 255, 0.3);
  margin: 0 auto;
  object-fit: cover;
}

.author-name {
  font-family: var(--font-heading);
  font-size: 1.85rem;
  font-weight: 800;
  color: #ffffff;
  margin-bottom: 0.35rem;
}

.author-title {
  color: var(--accent-cyan);
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 1.25rem;
}

.author-bio {
  color: var(--text-secondary);
  font-size: 1rem;
  line-height: 1.7;
  margin-bottom: 1.5rem;
}

.author-credentials {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.cred-badge {
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-subtle);
  padding: 5px 12px;
  border-radius: var(--radius-pill);
  font-size: 0.82rem;
  color: var(--text-secondary);
}

/* ==========================================================================
   BOOK SPECIFICATIONS / METADATA TABLE
   ========================================================================== */
.specs-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 1.5rem;
}

.specs-table tr {
  border-bottom: 1px solid var(--border-subtle);
}

.specs-table td {
  padding: 1rem;
  font-size: 0.95rem;
}

.specs-table td:first-child {
  font-weight: 600;
  color: var(--text-muted);
  width: 35%;
}

.specs-table td:last-child {
  color: var(--text-primary);
  font-weight: 500;
}

/* ==========================================================================
   ERRATA PAGE SPECIFIC STYLES
   ========================================================================== */
.errata-header-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 2.5rem;
  margin-bottom: 3rem;
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 2.5rem;
  align-items: center;
}

.errata-thumb {
  width: 130px;
  border-radius: var(--radius-sm);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.5);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.errata-stats-strip {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1.25rem;
  margin-bottom: 3rem;
}

.errata-stat-box {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  text-align: center;
}

.errata-stat-num {
  font-size: 1.85rem;
  font-weight: 800;
  font-family: var(--font-heading);
  line-height: 1;
  margin-bottom: 0.25rem;
}

.errata-stat-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

/* Errata Filter & Search */
.errata-filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2rem;
}

.search-input-wrapper {
  position: relative;
  flex: 1;
  max-width: 400px;
}

.search-input {
  width: 100%;
  padding: 10px 16px 10px 38px;
  background: #020617;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.95rem;
  outline: none;
  transition: border-color var(--transition-fast);
}

.search-input:focus {
  border-color: var(--accent-cyan);
  box-shadow: 0 0 10px rgba(0, 229, 255, 0.2);
}

.search-icon {
  position: absolute;
  left: 12px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
}

.filter-select {
  padding: 10px 16px;
  background: #020617;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.95rem;
  outline: none;
  cursor: pointer;
}

.filter-select:focus {
  border-color: var(--accent-cyan);
}

/* Errata Cards / Entries */
.errata-list {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  margin-bottom: 4rem;
}

.errata-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  transition: all var(--transition-fast);
}

.errata-card:hover {
  border-color: #475569;
}

.errata-card-header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
}

.errata-loc {
  font-weight: 700;
  font-size: 1.05rem;
  color: #ffffff;
}

.errata-loc-sub {
  color: var(--text-muted);
  font-size: 0.85rem;
  font-weight: normal;
  margin-left: 0.5rem;
}

.badge-status {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: var(--radius-pill);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.badge-confirmed {
  background: rgba(16, 185, 129, 0.15);
  color: #34d399;
  border: 1px solid rgba(16, 185, 129, 0.3);
}

.badge-fixed {
  background: rgba(59, 130, 246, 0.15);
  color: #60a5fa;
  border: 1px solid rgba(59, 130, 246, 0.3);
}

.badge-type {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 4px 10px;
  border-radius: var(--radius-pill);
  background: rgba(255, 255, 255, 0.06);
  color: var(--text-secondary);
}

.errata-diff {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  margin-bottom: 1rem;
}

.diff-box {
  padding: 1rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: 0.92rem;
  line-height: 1.6;
}

.diff-box.original {
  background: rgba(239, 68, 68, 0.08);
  border: 1px solid rgba(239, 68, 68, 0.25);
  color: #fca5a5;
}

.diff-box.corrected {
  background: rgba(16, 185, 129, 0.08);
  border: 1px solid rgba(16, 185, 129, 0.25);
  color: #a7f3d0;
}

.diff-label {
  font-weight: 700;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  margin-bottom: 0.5rem;
  display: block;
}

.diff-box.original .diff-label { color: #ef4444; }
.diff-box.corrected .diff-label { color: #10b981; }

.errata-note {
  font-size: 0.88rem;
  color: var(--text-muted);
  font-style: italic;
}

/* Errata Submission Form */
.submission-card {
  background: var(--bg-card);
  border: 1px solid var(--border-gold);
  border-radius: var(--radius-lg);
  padding: 2.5rem;
  box-shadow: var(--shadow-gold);
}

.form-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.25rem;
  margin-bottom: 1.25rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.form-group.full-width {
  grid-column: 1 / -1;
}

.form-label {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.form-input, .form-textarea, .form-select {
  padding: 10px 14px;
  background: #020617;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.95rem;
  outline: none;
  font-family: inherit;
  transition: border-color var(--transition-fast);
}

.form-input:focus, .form-textarea:focus, .form-select:focus {
  border-color: var(--accent-gold);
  box-shadow: 0 0 10px rgba(255, 193, 7, 0.2);
}

.form-textarea {
  min-height: 110px;
  resize: vertical;
}

/* ==========================================================================
   FOOTER
   ========================================================================== */
.footer {
  background: #020617;
  border-top: 1px solid var(--border-subtle);
  padding: 4rem 0 2rem;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 3rem;
  margin-bottom: 3rem;
}

.footer-brand {
  font-family: var(--font-heading);
  font-size: 1.15rem;
  font-weight: 800;
  color: #ffffff;
  margin-bottom: 0.75rem;
}

.footer-desc {
  color: var(--text-muted);
  font-size: 0.88rem;
  line-height: 1.6;
  max-width: 320px;
}

.footer-heading {
  font-family: var(--font-heading);
  font-size: 0.9rem;
  font-weight: 700;
  color: #ffffff;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  margin-bottom: 1rem;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.footer-links a {
  color: var(--text-muted);
  font-size: 0.88rem;
}

.footer-links a:hover {
  color: var(--accent-cyan);
}

.footer-bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  padding-top: 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 0.82rem;
}

/* ==========================================================================
   RESPONSIVE DESIGN (MEDIA QUERIES)
   ========================================================================== */
@media (max-width: 992px) {
  .hero-grid {
    grid-template-columns: 1fr;
    text-align: center;
    gap: 3rem;
  }
  
  .hero-badge-pill, .audience-callout {
    margin-left: auto;
    margin-right: auto;
  }
  
  .hero-ctas {
    justify-content: center;
  }
  
  .hero-meta-row {
    justify-content: center;
  }
  
  .author-card {
    grid-template-columns: 1fr;
    text-align: center;
    gap: 2rem;
  }
  
  .author-credentials {
    justify-content: center;
  }
  
  .errata-header-card {
    grid-template-columns: 1fr;
    text-align: center;
  }
  
  .errata-thumb {
    margin: 0 auto;
  }
  
  .errata-diff {
    grid-template-columns: 1fr;
  }
  
  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 768px) {
  .nav-links, .nav-cta {
    display: none;
  }
  
  .nav-toggle {
    display: block;
  }
  
  .nav-links.mobile-open {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: 72px;
    left: 0;
    right: 0;
    background: #0f172a;
    border-bottom: 1px solid var(--border-subtle);
    padding: 1.5rem;
    gap: 1.25rem;
  }
  
  .form-grid {
    grid-template-columns: 1fr;
  }
  
  .footer-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}