/* 
   ==========================================================================
   DESIGN SYSTEM & CUSTOM STYLES (MINIMALISTIC LIGHT THEME)
   Book: Mastering LangChain and LangGraph
   Author: Ankur Kulshreshtha
   ========================================================================== 
*/

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

/* Color Variables - Minimalistic Light Theme */
:root {
  --bg-primary: #F8FAFC;
  --bg-secondary: #FFFFFF;
  --bg-glass: rgba(255, 255, 255, 0.8);
  --bg-glass-hover: rgba(255, 255, 255, 0.95);
  
  --border-color: #E2E8F0;
  --border-glow: #CBD5E1;
  
  --accent-blue: #2563EB;
  --accent-indigo: #4F46E5;
  --accent-purple: #7C3AED;
  --accent-gradient: linear-gradient(135deg, #2563EB 0%, #4F46E5 50%, #7C3AED 100%);
  --text-gradient: linear-gradient(135deg, #0F172A 0%, #334155 100%);
  
  --text-primary: #0F172A;
  --text-secondary: #334155;
  --text-muted: #64748B;
  
  --shadow-neon: 0 10px 30px rgba(37, 99, 235, 0.08);
  --shadow-purple: 0 10px 30px rgba(124, 58, 237, 0.08);
  --shadow-card: 0 10px 25px rgba(0, 0, 0, 0.04);
  --shadow-modal: 0 20px 50px rgba(0, 0, 0, 0.1);
  
  --transition-smooth: all 0.4s cubic-bezier(0.16, 1, 0.3, 1);
  --transition-fast: all 0.2s ease;
}

/* Color Variables - Apress Black & Yellow Theme (Night Mode) */
body.night-mode {
  --bg-primary: #000000;
  --bg-secondary: #0C0C0D;
  --bg-glass: rgba(12, 12, 13, 0.85);
  --bg-glass-hover: rgba(18, 18, 20, 0.95);
  
  --border-color: #242427;
  --border-glow: #FFC20E;
  
  --accent-blue: #FFC20E; /* Apress Yellow */
  --accent-indigo: #F3AF00;
  --accent-purple: #D69900;
  --accent-gradient: linear-gradient(135deg, #FFC20E 0%, #F3AF00 100%);
  --text-gradient: linear-gradient(135deg, #FFFFFF 0%, #E2E8F0 100%);
  
  --text-primary: #FFFFFF;
  --text-secondary: #E4E4E7;
  --text-muted: #A1A1AA;
  
  --shadow-neon: 0 10px 30px rgba(255, 194, 14, 0.06);
  --shadow-purple: 0 10px 30px rgba(243, 175, 0, 0.06);
  --shadow-card: 0 10px 25px rgba(0, 0, 0, 0.5);
  --shadow-modal: 0 20px 50px rgba(0, 0, 0, 0.7);
}

/* Adjust glows in night-mode */
body.night-mode::before {
  background: radial-gradient(circle, rgba(255, 194, 14, 0.03) 0%, rgba(0, 0, 0, 0) 70%);
}

body.night-mode::after {
  background: radial-gradient(circle, rgba(243, 175, 0, 0.02) 0%, rgba(0, 0, 0, 0) 70%);
}

/* Night-Mode Specific Color Overrides */
body.night-mode #hero-badge {
  color: #FFFFFF !important;
  background: rgba(255, 255, 255, 0.08) !important;
  border-color: rgba(255, 255, 255, 0.15) !important;
}

body.night-mode .logo span,
body.night-mode .footer-logo span {
  background: none !important;
  -webkit-background-clip: initial !important;
  -webkit-text-fill-color: var(--accent-blue) !important;
  color: var(--accent-blue) !important;
}

body.night-mode .logo-icon {
  stroke: var(--accent-blue) !important;
}

body.night-mode #book-title,
body.night-mode .hero-meta .meta-val {
  color: var(--accent-blue) !important;
}

body.night-mode .meta-label,
body.night-mode .stat-label,
body.night-mode .toc-chapter-num {
  color: var(--text-muted) !important;
}

body.night-mode .version-notice {
  background: #18181B !important;
  border-color: #27272A !important;
  color: var(--text-secondary) !important;
}

body.night-mode .version-notice code {
  background: #27272A !important;
  border-color: #3F3F46 !important;
  color: var(--accent-blue) !important;
}

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

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

body {
  font-family: 'Inter', sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
  position: relative;
}

/* Soft Light Background Glows */
body::before {
  content: '';
  position: absolute;
  top: 0;
  left: 10%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(37, 99, 235, 0.04) 0%, rgba(255, 255, 255, 0) 70%);
  z-index: -1;
  pointer-events: none;
}

body::after {
  content: '';
  position: absolute;
  top: 1200px;
  right: 5%;
  width: 800px;
  height: 800px;
  background: radial-gradient(circle, rgba(124, 58, 237, 0.03) 0%, rgba(255, 255, 255, 0) 70%);
  z-index: -1;
  pointer-events: none;
}

/* Scrollbar Styles */
::-webkit-scrollbar {
  width: 10px;
}
::-webkit-scrollbar-track {
  background: var(--bg-primary);
}
::-webkit-scrollbar-thumb {
  background: #CBD5E1;
  border-radius: 5px;
  border: 2px solid var(--bg-primary);
}
::-webkit-scrollbar-thumb:hover {
  background: #94A3B8;
}

/* Selection Styles */
::selection {
  background-color: rgba(37, 99, 235, 0.15);
  color: var(--text-primary);
}

/* Typography */
h1, h2, h3, h4 {
  font-family: 'Outfit', sans-serif;
  font-weight: 700;
  letter-spacing: -0.02em;
}

p {
  color: var(--text-secondary);
  font-weight: 400;
}

/* Container */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

/* Navigation Bar */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background: var(--bg-glass);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  z-index: 1000;
  transition: var(--transition-smooth);
}

.navbar-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 80px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
  font-family: 'Outfit', sans-serif;
  font-weight: 800;
  font-size: 1.3rem;
  color: var(--text-primary);
}

.logo span {
  background: var(--text-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  color: var(--text-primary);
}

.logo-icon {
  width: 24px;
  height: 24px;
  stroke: var(--text-primary);
  stroke-width: 2.5;
  fill: none;
}

.nav-links {
  display: flex;
  gap: 2.5rem;
  list-style: none;
  align-items: center;
}

.nav-link {
  text-decoration: none;
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  transition: var(--transition-fast);
}

.nav-link:hover, .nav-link.active {
  color: var(--accent-blue);
}

/* General Button Styles */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.8rem 1.6rem;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: var(--transition-smooth);
  border: none;
}

.btn-primary {
  background: var(--text-primary);
  color: var(--bg-secondary);
  box-shadow: 0 4px 12px rgba(15, 23, 42, 0.08);
}

.btn-primary:hover {
  transform: translateY(-2px);
  background: #1E293B;
  box-shadow: 0 8px 20px rgba(15, 23, 42, 0.15);
}

.btn-secondary {
  background: var(--bg-secondary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  box-shadow: 0 2px 4px rgba(0,0,0,0.02);
}

.btn-secondary:hover {
  background: var(--bg-primary);
  border-color: var(--text-muted);
  transform: translateY(-2px);
}

.btn-sm {
  padding: 0.5rem 1.2rem;
  font-size: 0.85rem;
}

/* Nav Controls (Theme Toggle & Menu Toggle) */
.nav-controls {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.theme-toggle {
  background: none;
  border: 1px solid var(--border-color);
  width: 38px;
  height: 38px;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-primary);
  transition: var(--transition-fast);
}

.theme-toggle:hover {
  background: var(--bg-primary);
  border-color: var(--text-muted);
}

.theme-toggle svg {
  width: 18px;
  height: 18px;
  stroke: currentColor;
}

.theme-toggle .sun-icon {
  display: none;
}

.theme-toggle .moon-icon {
  display: block;
}

body.night-mode .theme-toggle .sun-icon {
  display: block;
}

body.night-mode .theme-toggle .moon-icon {
  display: none;
}

/* Mobile Menu Toggle */
.menu-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
}

.menu-toggle svg {
  width: 28px;
  height: 28px;
  stroke: var(--text-primary);
}

/* Hero Section */
.hero {
  padding: 160px 0 80px 0;
  position: relative;
  overflow: hidden;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 4rem;
  align-items: center;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(37, 99, 235, 0.06);
  border: 1px solid rgba(37, 99, 235, 0.15);
  color: var(--accent-blue);
  padding: 0.4rem 1rem;
  border-radius: 100px;
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: 1.5rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.hero-title {
  font-size: 3.5rem;
  line-height: 1.15;
  margin-bottom: 1.2rem;
  color: var(--text-primary);
}

.hero-subtitle {
  font-size: 1.35rem;
  color: var(--text-secondary);
  margin-bottom: 1.8rem;
  font-weight: 400;
  line-height: 1.45;
}

/* Tested Versions Callout Notice */
.version-notice {
  display: flex;
  align-items: center;
  gap: 0.7rem;
  background: #F1F5F9;
  border: 1px solid #E2E8F0;
  padding: 0.7rem 1.1rem;
  border-radius: 8px;
  margin-bottom: 2.2rem;
  font-size: 0.9rem;
  color: #0F172A;
  width: fit-content;
}

.notice-icon {
  width: 18px;
  height: 18px;
  stroke: #10B981;
  flex-shrink: 0;
}

.version-notice code {
  font-family: 'Fira Code', monospace;
  background: var(--bg-secondary);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  border: 1px solid #E2E8F0;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-primary);
}

.hero-meta {
  display: flex;
  gap: 2.5rem;
  margin-bottom: 2.2rem;
  flex-wrap: wrap;
}

.meta-item {
  display: flex;
  flex-direction: column;
}

.meta-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.2rem;
}

.meta-val {
  font-size: 1.1rem;
  font-weight: 500;
  color: var(--text-primary);
}

.hero-actions {
  display: flex;
  gap: 1.2rem;
  flex-wrap: wrap;
}

.book-viewport-wrapper {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
}

.book-instructions {
  font-size: 0.85rem;
  color: var(--text-secondary);
  background: var(--bg-secondary);
  padding: 0.4rem 1rem;
  border-radius: 100px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-card);
  pointer-events: none;
  user-select: none;
  animation: fadeIn 0.8s ease;
}

.book-instructions span {
  font-weight: 500;
}

.book-viewport {
  perspective: 1200px;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: all 0.4s ease;
}

/* Zoomed Lightbox state */
.book-viewport.zoomed {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  z-index: 2500;
  background: rgba(248, 250, 252, 0.94);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  display: flex;
  justify-content: center;
  align-items: center;
  cursor: zoom-out;
  margin: 0;
  padding: 0;
  animation: fadeIn 0.3s ease;
}

body.night-mode .book-viewport.zoomed {
  background: rgba(0, 0, 0, 0.95);
}

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

.book-viewport.zoomed::before {
  content: 'Close Preview';
  position: absolute;
  top: 2rem;
  right: 2rem;
  font-family: 'Outfit', sans-serif;
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-primary);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  padding: 0.5rem 1.2rem;
  border-radius: 8px;
  box-shadow: var(--shadow-card);
  cursor: pointer;
  z-index: 10;
}

.book-viewport.zoomed::after {
  content: 'Move mouse left & right to rotate 360°';
  position: absolute;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  font-family: inherit;
  font-size: 0.85rem;
  color: var(--text-muted);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  padding: 0.4rem 1rem;
  border-radius: 100px;
  box-shadow: var(--shadow-card);
  z-index: 10;
}

.book-container {
  position: relative;
  width: 300px;
  height: 420px;
  transform-style: preserve-3d;
  transform: rotateY(-15deg) rotateX(10deg);
  transition: transform 0.6s cubic-bezier(0.16, 1, 0.3, 1);
  cursor: pointer;
}

.book-viewport.zoomed .book-container {
  transform: scale(1.5) rotateY(0deg) rotateX(0deg);
}

.book-container.flipped {
  transform: rotateY(165deg) rotateX(10deg);
}

.book-3d {
  position: absolute;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
}

/* Front Cover */
.book-front {
  position: absolute;
  width: 300px;
  height: 420px;
  transform: translateZ(14px);
  box-shadow: 5px 5px 25px rgba(0, 0, 0, 0.08);
  z-index: 2;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.book-front img {
  width: 100%;
  height: 100%;
  object-fit: fill;
  border-radius: 2px 8px 8px 2px;
}

/* Back Cover */
.book-back {
  position: absolute;
  width: 300px;
  height: 420px;
  transform: rotateY(180deg) translateZ(14px);
  box-shadow: -5px 5px 25px rgba(0, 0, 0, 0.08);
  z-index: 1;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.book-back img {
  width: 100%;
  height: 100%;
  object-fit: fill;
  border-radius: 8px 2px 2px 8px;
}

/* Spine */
.book-spine {
  position: absolute;
  width: 28px;
  height: 420px;
  left: -14px;
  transform: rotateY(-90deg);
  z-index: 2;
}

.book-spine img {
  width: 100%;
  height: 100%;
  object-fit: fill;
  border-radius: 2px 0 0 2px;
}

/* Page Edges */
.book-pages {
  position: absolute;
  width: 28px;
  height: 416px;
  top: 2px;
  right: -14px;
  transform: rotateY(90deg);
  background: #FAF9F6;
  background-image: repeating-linear-gradient(
    90deg,
    rgba(0, 0, 0, 0.06) 0px,
    rgba(0, 0, 0, 0.06) 1px,
    transparent 1px,
    transparent 3px
  );
  border-left: 1px solid rgba(0, 0, 0, 0.05);
  border-right: 1px solid rgba(0, 0, 0, 0.05);
}

/* Shadow behind book */
.book-shadow {
  position: absolute;
  width: 300px;
  height: 30px;
  background: rgba(0, 0, 0, 0.06);
  bottom: -40px;
  left: 0;
  filter: blur(15px);
  transform: rotateX(85deg) translateZ(-40px);
  border-radius: 50%;
  pointer-events: none;
}

/* Stats/Highlights Bar */
.stats-section {
  padding: 40px 0;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 2rem;
  text-align: center;
}

.stat-card {
  padding: 1.2rem;
}

.stat-number {
  font-size: 2.8rem;
  font-family: 'Outfit', sans-serif;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1;
  margin-bottom: 0.5rem;
}

.stat-label {
  font-size: 0.85rem;
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Section Common Layout */
.section {
  padding: 90px 0;
}

.section-header {
  text-align: center;
  max-width: 700px;
  margin: 0 auto 4rem auto;
}

.section-title {
  font-size: 2.4rem;
  margin-bottom: 0.8rem;
  color: var(--text-primary);
}

.section-title span {
  color: var(--accent-blue);
}

.section-desc {
  font-size: 1.05rem;
  color: var(--text-secondary);
}

/* Grid Layout for Learn Section */
.learn-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 2.5rem;
}

.learn-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  padding: 2.5rem;
  border-radius: 16px;
  transition: var(--transition-smooth);
  position: relative;
  overflow: hidden;
  box-shadow: var(--shadow-card);
}

.learn-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: var(--accent-gradient);
  opacity: 0;
  transition: var(--transition-smooth);
}

.learn-card:hover {
  transform: translateY(-5px);
  border-color: var(--border-glow);
  box-shadow: var(--shadow-neon);
}

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

.learn-icon-wrapper {
  width: 50px;
  height: 50px;
  background: rgba(37, 99, 235, 0.05);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1.5rem;
  border: 1px solid rgba(37, 99, 235, 0.12);
}

.learn-icon {
  width: 24px;
  height: 24px;
  stroke: var(--accent-blue);
  stroke-width: 2;
  fill: none;
}

.learn-card h3 {
  font-size: 1.35rem;
  margin-bottom: 0.8rem;
  color: var(--text-primary);
}

.learn-card p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* Table of Contents Section */
.toc-container {
  display: block;
  max-width: 800px;
  margin: 0 auto;
}

/* TOC Contents display */
.toc-content-wrapper {
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.toc-part-group {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 2rem;
  transition: var(--transition-smooth);
  box-shadow: var(--shadow-card);
}

.toc-part-group:hover {
  border-color: var(--border-glow);
}

.toc-part-header {
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.8rem;
  margin-bottom: 1.2rem;
}

.toc-part-num {
  font-family: 'Fira Code', monospace;
  font-size: 0.8rem;
  color: var(--accent-indigo);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  display: block;
  margin-bottom: 0.2rem;
}

.toc-part-title {
  font-size: 1.45rem;
  color: var(--text-primary);
}

.toc-chapter-list {
  display: flex;
  flex-direction: column;
  gap: 0.8rem;
}

.toc-chapter-item {
  display: grid;
  grid-template-columns: 100px 1fr;
  align-items: center;
  padding: 0.8rem 1rem;
  border-radius: 8px;
  background: var(--bg-primary);
  border: 1px solid rgba(0, 0, 0, 0.01);
  transition: var(--transition-fast);
}

.toc-chapter-item:hover {
  background: var(--bg-secondary);
  border-color: var(--border-color);
  transform: translateX(3px);
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.02);
}

.toc-chapter-num {
  font-family: 'Fira Code', monospace;
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-muted);
}

.toc-chapter-title {
  font-size: 1.05rem;
  font-weight: 500;
  color: var(--text-primary);
}

/* Audience Section */
.audience-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2rem;
}

.audience-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 2.5rem 2rem;
  text-align: center;
  transition: var(--transition-smooth);
  box-shadow: var(--shadow-card);
}

.audience-card:hover {
  transform: translateY(-5px);
  border-color: var(--accent-purple);
  box-shadow: var(--shadow-purple);
}

.audience-avatar {
  width: 64px;
  height: 64px;
  background: rgba(124, 58, 237, 0.05);
  border: 1px solid rgba(124, 58, 237, 0.12);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 1.5rem auto;
}

.audience-avatar svg {
  width: 28px;
  height: 28px;
  stroke: var(--accent-purple);
  stroke-width: 2;
  fill: none;
}

.audience-card h3 {
  font-size: 1.25rem;
  margin-bottom: 0.8rem;
  color: var(--text-primary);
}

.audience-card p {
  font-size: 0.9rem;
  color: var(--text-secondary);
}

/* Author Section */
.author {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.author-grid {
  display: grid;
  grid-template-columns: 0.7fr 1.3fr;
  gap: 4rem;
  align-items: center;
}

.author-image-wrapper {
  position: relative;
  display: flex;
  justify-content: center;
}

.author-avatar {
  width: 240px;
  height: 240px;
  object-fit: cover;
  border: 1px solid var(--border-color);
  border-radius: 24px;
  box-shadow: var(--shadow-card);
  transition: var(--transition-smooth);
}

.author-avatar:hover {
  transform: scale(1.02);
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.08);
}

.author-details h3 {
  font-size: 2rem;
  margin-bottom: 0.4rem;
  color: var(--text-primary);
}

.author-title {
  color: var(--accent-blue);
  font-weight: 600;
  font-size: 0.9rem;
  margin-bottom: 1.2rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  display: inline-block;
}

.author-bio {
  font-size: 1rem;
  line-height: 1.65;
  margin-bottom: 1.8rem;
  color: var(--text-secondary);
}

.author-bio a {
  color: var(--accent-blue);
  text-decoration: none;
  font-weight: 600;
  transition: var(--transition-fast);
}

.author-bio a:hover {
  text-decoration: underline;
  color: var(--accent-indigo);
}

.author-socials {
  display: flex;
  gap: 1rem;
}

.social-link {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  transition: var(--transition-fast);
  background: var(--bg-primary);
}

.social-link:hover {
  color: var(--text-primary);
  border-color: var(--text-muted);
  background: var(--bg-secondary);
  transform: translateY(-2px);
}

.social-link svg {
  width: 20px;
  height: 20px;
  stroke: currentColor;
  stroke-width: 2;
  fill: none;
}

/* Call to Action Section (Newsletter) */
.cta-section {
  position: relative;
  overflow: hidden;
}

.cta-box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 24px;
  padding: 4rem;
  text-align: center;
  box-shadow: var(--shadow-card);
  position: relative;
}

.cta-box h2 {
  font-size: 2.2rem;
  margin-bottom: 0.8rem;
  color: var(--text-primary);
}

.cta-box p {
  max-width: 600px;
  margin: 0 auto 2.2rem auto;
  font-size: 1.05rem;
  color: var(--text-secondary);
}

/* Subscription Form */
.cta-form {
  max-width: 500px;
  margin: 0 auto;
  display: flex;
  gap: 0.8rem;
}

.cta-form input {
  flex: 1;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 0.9rem 1.2rem;
  color: var(--text-primary);
  font-family: inherit;
  font-size: 0.95rem;
  outline: none;
  transition: var(--transition-fast);
}

.cta-form input:focus {
  border-color: var(--text-primary);
  background: var(--bg-secondary);
  box-shadow: 0 0 0 3px rgba(15, 23, 42, 0.05);
}

/* Footer styling */
.footer {
  padding: 40px 0;
  border-top: 1px solid var(--border-color);
  text-align: center;
  background: var(--bg-secondary);
}

.footer-logo {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
  font-family: 'Outfit', sans-serif;
  font-weight: 800;
  font-size: 1.2rem;
  color: var(--text-primary);
  margin-bottom: 0.8rem;
}

.footer p {
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* Modal Styling */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.4);
  backdrop-filter: blur(4px);
  z-index: 2000;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s ease;
}

.modal.active {
  opacity: 1;
  pointer-events: all;
}

.modal-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 20px;
  width: 90%;
  max-width: 480px;
  padding: 2.5rem;
  position: relative;
  transform: scale(0.9);
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1);
  box-shadow: var(--shadow-modal);
}

.modal.active .modal-card {
  transform: scale(1);
}

.modal-close {
  position: absolute;
  top: 1.5rem;
  right: 1.5rem;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--text-muted);
  transition: var(--transition-fast);
}

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

.modal-close svg {
  width: 24px;
  height: 24px;
  stroke: currentColor;
  stroke-width: 2;
}

.modal-header {
  text-align: center;
  margin-bottom: 2rem;
}

.modal-title {
  font-size: 1.7rem;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.modal-desc {
  font-size: 0.95rem;
  color: var(--text-secondary);
}

/* Toast styling for notifications */
.toast-container {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  z-index: 3000;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.toast {
  background: var(--bg-secondary);
  border: 1px solid #10B981;
  box-shadow: 0 10px 30px rgba(16, 185, 129, 0.08);
  border-radius: 8px;
  padding: 1rem 1.5rem;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.8rem;
  transform: translateY(100px);
  opacity: 0;
  transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.toast.show {
  transform: translateY(0);
  opacity: 1;
}

.toast-icon {
  width: 20px;
  height: 20px;
  stroke: #10B981;
  stroke-width: 2.5;
  fill: none;
}

/* Response/Utility classes */
.hidden {
  display: none !important;
}

/* Responsive Media Queries */
@media (max-width: 1024px) {
  .hero-grid {
    grid-template-columns: 1fr;
    gap: 3rem;
    text-align: center;
  }
  
  .hero-title {
    font-size: 2.8rem;
  }
  
  .hero-meta {
    justify-content: center;
  }
  
  .hero-actions {
    justify-content: center;
  }
  
  .version-notice {
    margin-left: auto;
    margin-right: auto;
  }
  
  .toc-container {
    grid-template-columns: 1fr;
    gap: 2.5rem;
  }
  
  .toc-controls {
    position: static;
  }
  
  .author-grid {
    grid-template-columns: 1fr;
    gap: 3rem;
    text-align: center;
  }
  
  .author-image-wrapper {
    order: -1;
  }
  
  .author-socials {
    justify-content: center;
  }
}

@media (max-width: 768px) {
  html {
    font-size: 15px;
  }
  
  .navbar-container {
    flex-direction: column;
    height: auto;
    padding: 0.8rem 1rem;
    gap: 0.6rem;
  }

  .logo {
    font-size: 1rem;
    width: 100%;
    justify-content: center;
    gap: 0.4rem;
  }

  .logo span {
    white-space: normal;
    text-align: left;
    font-size: 0.95rem;
    line-height: 1.25;
    max-width: calc(100% - 32px);
  }

  .logo-icon {
    flex-shrink: 0;
  }

  .nav-controls {
    width: 100%;
    justify-content: center;
    gap: 1.5rem;
  }
  
  .nav-links {
    display: none; /* Mobile menu collapsed by default, toggled by JS */
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    flex-direction: column;
    padding: 2rem;
    gap: 1.5rem;
    text-align: center;
    box-shadow: var(--shadow-card);
  }
  
  .nav-links.active {
    display: flex;
  }
  
  .menu-toggle {
    display: block;
  }
  
  .stats-grid {
    grid-template-columns: repeat(2, 1fr);
  }
  
  .learn-grid {
    grid-template-columns: 1fr;
  }
  
  .audience-grid {
    grid-template-columns: 1fr;
  }
  
  .cta-box {
    padding: 3rem 1.5rem;
  }
  
  .cta-form {
    flex-direction: column;
  }

  /* Responsive book scale when zoomed in */
  .book-viewport.zoomed .book-container {
    transform: scale(1.15) rotateY(0deg) rotateX(0deg);
  }

  .book-viewport.zoomed::after {
    content: 'Swipe left & right to rotate 360°';
  }
}

@media (max-width: 480px) {
  .hero-title {
    font-size: 2.2rem;
  }
  
  .stats-grid {
    grid-template-columns: 1fr;
  }

  /* Mobile-specific book scale when zoomed in */
  .book-viewport.zoomed .book-container {
    transform: scale(0.85) rotateY(0deg) rotateX(0deg);
  }

  .book-viewport.zoomed::before {
    top: 1rem;
    right: 1rem;
    padding: 0.4rem 0.8rem;
    font-size: 0.8rem;
  }

  .book-viewport.zoomed::after {
    bottom: 1rem;
    font-size: 0.8rem;
    padding: 0.4rem 0.8rem;
  }
}