/* ============================================
   JEE Notes - Main Stylesheet
   A clean, modern design for interactive learning
   ============================================ */

/* ---------- CSS Variables ---------- */
:root {
  /* Typography */
  --font-sans: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  
  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  
  /* Layout */
  --max-width: 1200px;
  --content-width: 800px;
  --header-height: 4rem;
  --toc-width: 260px;
  
  /* Border radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  
  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;
}

/* Light theme */
[data-theme="light"] {
  --bg-primary: #fafafa;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f4f4f5;
  --bg-code: #f4f4f5;
  
  --text-primary: #18181b;
  --text-secondary: #52525b;
  --text-tertiary: #71717a;
  --text-muted: #a1a1aa;
  
  --border-color: #e4e4e7;
  --border-subtle: #f4f4f5;
  
  --accent-physics: #3b82f6;
  --accent-chemistry: #10b981;
  --accent-math: #f59e0b;
  --accent-primary: #6366f1;
  --accent-glow: rgba(99, 102, 241, 0.15);
  
  --gradient-start: #6366f1;
  --gradient-end: #a855f7;
  
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
}

/* Dark theme (default) */
[data-theme="dark"] {
  --bg-primary: #09090b;
  --bg-secondary: #18181b;
  --bg-tertiary: #27272a;
  --bg-code: #1e1e2e;
  
  --text-primary: #fafafa;
  --text-secondary: #a1a1aa;
  --text-tertiary: #71717a;
  --text-muted: #52525b;
  
  --border-color: #27272a;
  --border-subtle: #1f1f23;
  
  --accent-physics: #60a5fa;
  --accent-chemistry: #34d399;
  --accent-math: #fbbf24;
  --accent-primary: #818cf8;
  --accent-glow: rgba(129, 140, 248, 0.2);
  
  --gradient-start: #818cf8;
  --gradient-end: #c084fc;
  
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.5);
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ---------- Typography ---------- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--text-primary);
}

h1 { font-size: 2.5rem; letter-spacing: -0.02em; }
h2 { font-size: 1.875rem; letter-spacing: -0.01em; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }
h5 { font-size: 1.125rem; }
h6 { font-size: 1rem; }

p {
  margin-bottom: var(--space-md);
  color: var(--text-secondary);
}

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

a:hover {
  color: var(--gradient-end);
}

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

/* ---------- Header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
  background: rgba(var(--bg-primary), 0.9);
}

[data-theme="dark"] .site-header {
  background: rgba(9, 9, 11, 0.9);
}

[data-theme="light"] .site-header {
  background: rgba(250, 250, 250, 0.9);
}

.nav-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-lg);
  height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  text-decoration: none;
  transition: transform var(--transition-base);
}

.site-logo:hover {
  transform: scale(1.03);
}

.logo-text {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.logo-accent {
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: var(--space-xl);
}

.nav-links {
  display: flex;
  list-style: none;
  gap: var(--space-lg);
}

.nav-link {
  position: relative;
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.95rem;
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-md);
  transition: color var(--transition-base), transform var(--transition-base);
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 2px;
  left: 50%;
  width: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--gradient-start), var(--gradient-end));
  border-radius: 1px;
  transform: translateX(-50%);
  transition: width var(--transition-base);
}

.nav-link:hover {
  color: var(--text-primary);
  transform: translateY(-2px);
}

.nav-link:hover::after {
  width: 70%;
}

.nav-link.active {
  color: var(--text-primary);
}

.nav-link.active::after {
  width: 70%;
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-sm);
}

.hamburger {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--text-primary);
  position: relative;
  transition: var(--transition-fast);
}

.hamburger::before,
.hamburger::after {
  content: '';
  position: absolute;
  width: 24px;
  height: 2px;
  background: var(--text-primary);
  transition: var(--transition-fast);
}

.hamburger::before { top: -7px; }
.hamburger::after { top: 7px; }

/* Theme Toggle */
.theme-toggle {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--space-sm);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-secondary);
  transition: all var(--transition-base);
}

.theme-toggle:hover {
  background: var(--bg-secondary);
  color: var(--text-primary);
  transform: rotate(15deg) scale(1.1);
}

.theme-toggle:active {
  transform: rotate(0deg) scale(0.95);
}

[data-theme="dark"] .icon-sun { display: block; }
[data-theme="dark"] .icon-moon { display: none; }
[data-theme="light"] .icon-sun { display: none; }
[data-theme="light"] .icon-moon { display: block; }

/* ---------- Main Content ---------- */
.main-content {
  flex: 1;
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-2xl) var(--space-lg);
}

/* ---------- Hero Section ---------- */
.hero {
  display: grid;
  grid-template-columns: 1.3fr 1fr;
  gap: var(--space-3xl);
  align-items: center;
  padding: var(--space-3xl) 0;
  min-height: calc(60vh - var(--header-height));
}

.hero-title {
  font-size: 3.5rem;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-lg);
}

.gradient-text {
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-description {
  font-size: 1.25rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-xl);
  max-width: 500px;
}

.hero-actions {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--radius-md);
  font-weight: 500;
  font-size: 1rem;
  transition: all var(--transition-fast);
  cursor: pointer;
  border: none;
}

.btn-primary {
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  color: white;
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 20px var(--accent-glow);
  color: white;
}

.btn-secondary {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

.btn-secondary:hover {
  background: var(--bg-secondary);
  border-color: var(--accent-primary);
}

.hero-visual {
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero-image {
  width: 100%;
  max-width: 500px;
  height: auto;
  filter: drop-shadow(0 10px 30px rgba(99, 102, 241, 0.15));
  transition: transform var(--transition-base);
}

.hero-image:hover {
  transform: scale(1.02);
}

[data-theme="dark"] .hero-image {
  filter: drop-shadow(0 10px 30px rgba(99, 102, 241, 0.25));
}

/* ---------- Section Headings ---------- */
.section-heading {
  font-size: 1.75rem;
  font-weight: 600;
  margin-bottom: var(--space-xl);
  text-align: center;
}

/* ---------- Subjects Grid ---------- */
.subjects-section {
  padding: var(--space-3xl) 0;
}

.subjects-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-lg);
}

.subject-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  text-decoration: none;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

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

.subject-physics::before { background: var(--accent-physics); }
.subject-chemistry::before { background: var(--accent-chemistry); }
.subject-math::before { background: var(--accent-math); }

.subject-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: transparent;
}

.subject-card:hover::before {
  height: 4px;
}

.subject-icon {
  margin-bottom: var(--space-md);
  color: var(--text-secondary);
}

.subject-icon .icon {
  width: 32px;
  height: 32px;
}

.subject-physics .subject-icon { color: var(--accent-physics); }
.subject-chemistry .subject-icon { color: var(--accent-chemistry); }
.subject-math .subject-icon { color: var(--accent-math); }

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

.subject-card p {
  font-size: 0.9rem;
  color: var(--text-tertiary);
  margin-bottom: var(--space-md);
}

.subject-link {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--accent-primary);
}

/* ---------- Cards Grid ---------- */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--space-lg);
}

.card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  transition: all var(--transition-base);
  overflow: hidden;
}

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

.card-link {
  display: block;
  padding: var(--space-xl);
  text-decoration: none;
}

.card-subject {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-primary);
  margin-bottom: var(--space-sm);
}

.card-title {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-sm);
}

.card-description {
  font-size: 0.9rem;
  color: var(--text-tertiary);
  margin-bottom: var(--space-md);
  line-height: 1.5;
}

.card-meta {
  display: flex;
  gap: var(--space-md);
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* ---------- Features Section ---------- */
.features-section {
  padding: var(--space-3xl) 0;
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-lg);
}

.feature {
  text-align: center;
  padding: var(--space-xl);
}

.feature-icon {
  margin-bottom: var(--space-md);
  color: var(--accent-primary);
}

.feature-icon .icon {
  width: 28px;
  height: 28px;
}

.feature h3 {
  font-size: 1rem;
  margin-bottom: var(--space-sm);
}

.feature p {
  font-size: 0.9rem;
  color: var(--text-tertiary);
}

/* ---------- Breadcrumbs ---------- */
.breadcrumbs {
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-md);
  border-bottom: 1px solid var(--border-color);
}

.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-xs);
  list-style: none;
  padding: 0;
  margin: 0;
}

.breadcrumb-item {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

.breadcrumb-link {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.875rem;
  font-weight: 500;
  padding: var(--space-xs) var(--space-sm);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}

.breadcrumb-link:hover {
  color: var(--accent-primary);
  background: var(--bg-tertiary);
}

.breadcrumb-home {
  padding: var(--space-xs);
}

.breadcrumb-home svg {
  color: var(--text-tertiary);
}

.breadcrumb-home:hover svg {
  color: var(--accent-primary);
}

.breadcrumb-separator {
  color: var(--text-muted);
  flex-shrink: 0;
}

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

.breadcrumb-text {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
  padding: var(--space-xs) var(--space-sm);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

@media (max-width: 640px) {
  .breadcrumb-link,
  .breadcrumb-text {
    font-size: 0.8rem;
    padding: var(--space-xs);
  }
  
  .breadcrumbs {
    margin-bottom: var(--space-lg);
  }
}

/* ---------- Article Styles ---------- */
.article {
  max-width: var(--content-width);
  margin: 0 auto;
}

.article-container {
  display: flex;
  gap: var(--space-3xl);
}

.article-header {
  margin-bottom: var(--space-2xl);
  padding-bottom: var(--space-xl);
  border-bottom: 1px solid var(--border-color);
}

.article-meta {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-md);
  flex-wrap: wrap;
}

.article-subject {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-primary);
  background: var(--accent-glow);
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--radius-sm);
}

.article-tags {
  display: flex;
  gap: var(--space-sm);
}

.tag {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  background: var(--bg-tertiary);
  padding: var(--space-xs) var(--space-sm);
  border-radius: var(--radius-sm);
}

.article-title {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.article-description {
  font-size: 1.25rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
}

.article-info {
  display: flex;
  gap: var(--space-md);
  font-size: 0.9rem;
  color: var(--text-muted);
}

/* Table of Contents */
.toc-sidebar {
  position: sticky;
  top: calc(var(--header-height) + var(--space-xl));
  align-self: flex-start;
  width: var(--toc-width);
  flex-shrink: 0;
  order: 0;
}

.article-content {
  order: 1;
  flex: 1;
  min-width: 0;
}

.toc {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
}

.toc-title {
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: var(--space-md);
  color: var(--text-primary);
}

.toc ul {
  list-style: none;
}

.toc li {
  margin-bottom: var(--space-sm);
}

.toc a {
  font-size: 0.85rem;
  color: var(--text-tertiary);
  display: block;
  padding: var(--space-xs) 0;
  border-left: 2px solid transparent;
  padding-left: var(--space-md);
  transition: all var(--transition-fast);
}

.toc a:hover,
.toc a.active {
  color: var(--accent-primary);
  border-left-color: var(--accent-primary);
}

.toc ul ul {
  padding-left: var(--space-md);
}

/* Article Content - h2 styles */
.article-content h2 {
  font-size: 1.75rem;
  margin-top: var(--space-2xl);
  margin-bottom: var(--space-md);
  padding-top: var(--space-lg);
  border-top: 1px solid var(--border-subtle);
}

.article-content h2:first-child {
  margin-top: 0;
  padding-top: 0;
  border-top: none;
}

.article-content h3 {
  font-size: 1.375rem;
  margin-top: var(--space-xl);
  margin-bottom: var(--space-md);
}

.article-content h4 {
  font-size: 1.125rem;
  margin-top: var(--space-lg);
  margin-bottom: var(--space-sm);
}

.article-content p {
  margin-bottom: var(--space-md);
}

.article-content ul,
.article-content ol {
  margin-bottom: var(--space-md);
  padding-left: var(--space-xl);
}

.article-content li {
  margin-bottom: var(--space-sm);
  color: var(--text-secondary);
}

.article-content li::marker {
  color: var(--accent-primary);
}

.article-content blockquote {
  border-left: 3px solid var(--accent-primary);
  padding-left: var(--space-lg);
  margin: var(--space-lg) 0;
  font-style: italic;
  color: var(--text-secondary);
}

.article-content img {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius-md);
  margin: var(--space-lg) 0;
}

.article-content table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-lg) 0;
  font-size: 0.9rem;
}

.article-content th,
.article-content td {
  padding: var(--space-md);
  text-align: left;
  border: 1px solid var(--border-color);
}

.article-content th {
  background: var(--bg-tertiary);
  font-weight: 600;
}

.article-content tr:nth-child(even) {
  background: var(--bg-secondary);
}

/* Code Blocks */
.article-content code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--bg-code);
  padding: 0.15em 0.4em;
  border-radius: var(--radius-sm);
  color: var(--accent-primary);
}

.article-content pre {
  background: var(--bg-code);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  overflow-x: auto;
  margin: var(--space-lg) 0;
  border: 1px solid var(--border-color);
}

.article-content pre code {
  background: none;
  padding: 0;
  color: var(--text-primary);
  font-size: 0.875rem;
  line-height: 1.6;
}

/* Mermaid Diagrams */
.mermaid {
  background: var(--bg-secondary);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  margin: var(--space-lg) 0;
  display: flex;
  justify-content: center;
  border: 1px solid var(--border-color);
}

/* Math */
.katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  padding: var(--space-md) 0;
}

/* Article Navigation */
/* ---------- Subtopic Navigation ---------- */
.subtopic-nav {
  margin-top: var(--space-3xl);
  padding-top: var(--space-xl);
  border-top: 2px solid var(--border-color);
}

.subtopic-nav-inner {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: var(--space-md);
  align-items: stretch;
}

.subtopic-nav-link {
  display: flex;
  flex-direction: column;
  padding: var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.subtopic-nav-link:hover {
  background: var(--bg-tertiary);
  border-color: var(--accent-primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.subtopic-nav-prev {
  text-align: left;
}

.subtopic-nav-next {
  text-align: right;
}

.subtopic-nav-parent {
  text-align: center;
  background: var(--bg-tertiary);
  border-style: dashed;
}

.subtopic-nav-placeholder {
  visibility: hidden;
}

.subtopic-nav-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
  margin-bottom: var(--space-xs);
}

.subtopic-nav-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
}

@media (max-width: 768px) {
  .subtopic-nav-inner {
    grid-template-columns: 1fr 1fr;
  }
  
  .subtopic-nav-parent {
    grid-column: 1 / -1;
    order: -1;
  }
}

/* ---------- Article Navigation ---------- */
.article-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-lg);
  margin-top: var(--space-3xl);
  padding-top: var(--space-xl);
  border-top: 1px solid var(--border-color);
}

.nav-link {
  display: flex;
  flex-direction: column;
  padding: var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.nav-link:hover {
  border-color: var(--accent-primary);
  transform: translateY(-2px);
}

.nav-prev {
  align-items: flex-start;
}

.nav-next {
  align-items: flex-end;
  text-align: right;
}

.nav-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: var(--space-xs);
}

.nav-title {
  font-weight: 500;
  color: var(--text-primary);
}

/* ---------- Section List ---------- */
.section-list {
  padding: 0;
}

.section-header {
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid var(--border-color);
}

.section-title {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.section-description {
  font-size: 1.125rem;
  color: var(--text-secondary);
}

.no-content {
  text-align: center;
  color: var(--text-tertiary);
  padding: var(--space-3xl);
}

/* ---------- Footer ---------- */
.site-footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: var(--space-3xl) var(--space-lg) var(--space-xl);
  margin-top: auto;
}

.footer-content {
  max-width: var(--max-width);
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  gap: var(--space-2xl);
  margin-bottom: var(--space-2xl);
}

.footer-tagline {
  color: var(--text-tertiary);
  font-size: 0.9rem;
  margin-top: var(--space-sm);
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2xl);
}

.footer-section {
  min-width: 140px;
}

.footer-section h4 {
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: var(--space-md);
  color: var(--text-primary);
}

.footer-section ul {
  list-style: none;
}

.footer-section li {
  margin-bottom: var(--space-sm);
}

.footer-section a {
  color: var(--text-tertiary);
  font-size: 0.9rem;
}

.footer-section a:hover {
  color: var(--text-primary);
}

.footer-section h4 .icon {
  display: inline-block;
  vertical-align: middle;
  margin-right: var(--space-xs);
  opacity: 0.7;
}

/* PYQ Quick Access Years */
.pyq-years {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  margin-top: var(--space-sm);
  align-items: center;
}

.pyq-years .pyq-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-right: var(--space-xs);
}

.pyq-years a {
  display: inline-block;
  padding: 0.2rem 0.5rem;
  font-size: 0.75rem;
  background: var(--bg-tertiary);
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.pyq-years a:hover {
  background: var(--accent-primary);
  color: var(--bg-primary);
}

/* Inline icons in content */
.inline-icon {
  display: inline-block;
  vertical-align: middle;
  margin-right: 0.25em;
}

.icon-heading {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

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

.footer-bottom {
  max-width: var(--max-width);
  margin: 0 auto;
  padding-top: var(--space-lg);
  border-top: 1px solid var(--border-color);
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-muted);
}

.footer-bottom a {
  color: var(--text-tertiary);
}

/* ---------- Responsive Design ---------- */
@media (max-width: 1024px) {
  .hero {
    grid-template-columns: 1fr;
    text-align: center;
  }
  
  .hero-description {
    margin-left: auto;
    margin-right: auto;
  }
  
  .hero-actions {
    justify-content: center;
  }
  
  .hero-visual {
    order: -1;
  }
  
  .subjects-grid {
    grid-template-columns: 1fr;
  }
  
  .features-grid {
    grid-template-columns: repeat(2, 1fr);
  }
  
  .toc-sidebar {
    display: none;
  }
  
  .article {
    max-width: 100%;
  }
}

@media (max-width: 768px) {
  .nav-toggle {
    display: block;
  }
  
  .nav-menu {
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    bottom: 0;
    background: var(--bg-primary);
    flex-direction: column;
    padding: var(--space-xl);
    gap: var(--space-lg);
    transform: translateX(100%);
    transition: transform var(--transition-base);
  }
  
  .nav-menu.open {
    transform: translateX(0);
  }
  
  .nav-links {
    flex-direction: column;
    width: 100%;
  }
  
  .nav-link {
    padding: var(--space-md);
    text-align: center;
  }
  
  .hero-title {
    font-size: 2.5rem;
  }
  
  .features-grid {
    grid-template-columns: 1fr;
  }
  
  .cards-grid {
    grid-template-columns: 1fr;
  }
  
  .article-nav {
    grid-template-columns: 1fr;
  }
  
  .footer-content {
    flex-direction: column;
    text-align: center;
  }
  
  .footer-links {
    justify-content: center;
  }
}

/* ---------- Interactive Elements ---------- */
/* Custom interactive containers */
.interactive-container {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin: var(--space-xl) 0;
}

.interactive-container h3 {
  font-size: 1.125rem;
  margin-bottom: var(--space-md);
}

/* Callouts / Admonitions */
.callout {
  padding: var(--space-lg);
  border-radius: var(--radius-md);
  margin: var(--space-lg) 0;
  border-left: 4px solid;
}

.callout-note {
  background: rgba(59, 130, 246, 0.1);
  border-color: var(--accent-physics);
}

.callout-note .callout-title { color: var(--accent-physics); }

.callout-tip {
  background: rgba(16, 185, 129, 0.1);
  border-color: var(--accent-chemistry);
}

.callout-tip .callout-title { color: var(--accent-chemistry); }

.callout-warning {
  background: rgba(245, 158, 11, 0.1);
  border-color: var(--accent-math);
}

.callout-warning .callout-title { color: var(--accent-math); }

.callout-important {
  background: rgba(239, 68, 68, 0.1);
  border-color: #ef4444;
}

.callout-important .callout-title { color: #ef4444; }

.callout-check {
  background: rgba(16, 185, 129, 0.1);
  border-color: var(--accent-chemistry);
}

.callout-check .callout-title { color: var(--accent-chemistry); }

.callout-title {
  font-weight: 600;
  margin-bottom: var(--space-sm);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.callout-title .icon {
  flex-shrink: 0;
}

.callout-content p:last-child {
  margin-bottom: 0;
}

/* Tabs */
.tabs {
  margin: var(--space-lg) 0;
}

.tab-list {
  display: flex;
  border-bottom: 1px solid var(--border-color);
  gap: var(--space-sm);
}

.tab-button {
  padding: var(--space-md) var(--space-lg);
  background: none;
  border: none;
  cursor: pointer;
  color: var(--text-tertiary);
  font-weight: 500;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  transition: all var(--transition-fast);
}

.tab-button:hover {
  color: var(--text-primary);
}

.tab-button.active {
  color: var(--accent-primary);
  border-bottom-color: var(--accent-primary);
}

.tab-content {
  display: none;
  padding: var(--space-lg) 0;
}

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

/* ---------- Animations ---------- */
@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.article-content > * {
  animation: fadeIn 0.4s ease forwards;
}

.card {
  animation: fadeIn 0.4s ease forwards;
}

/* Stagger animations */
.cards-grid .card:nth-child(1) { animation-delay: 0.05s; }
.cards-grid .card:nth-child(2) { animation-delay: 0.1s; }
.cards-grid .card:nth-child(3) { animation-delay: 0.15s; }
.cards-grid .card:nth-child(4) { animation-delay: 0.2s; }
.cards-grid .card:nth-child(5) { animation-delay: 0.25s; }
.cards-grid .card:nth-child(6) { animation-delay: 0.3s; }

/* ---------- Box Shortcode Styles ---------- */
.box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  margin: var(--space-lg) 0;
}

.box-formula {
  border-left: 4px solid var(--accent-primary);
  background: linear-gradient(to right, var(--accent-glow), transparent);
}

.box-definition {
  border-left: 4px solid var(--accent-chemistry);
  background: linear-gradient(to right, rgba(16, 185, 129, 0.1), transparent);
}

.box-theorem {
  border-left: 4px solid var(--accent-math);
  background: linear-gradient(to right, rgba(245, 158, 11, 0.1), transparent);
}

.box-example {
  border-left: 4px solid var(--accent-physics);
  background: linear-gradient(to right, rgba(59, 130, 246, 0.1), transparent);
}

.box-title {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-md);
}

.box-content {
  color: var(--text-secondary);
}

.box-content p:last-child {
  margin-bottom: 0;
}

/* ---------- Collapse/Accordion Styles ---------- */
.collapse {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  margin: var(--space-md) 0;
  overflow: hidden;
}

.collapse-title {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-lg);
  cursor: pointer;
  font-weight: 600;
  color: var(--text-primary);
  transition: all var(--transition-fast);
  list-style: none;
}

.collapse-title::-webkit-details-marker {
  display: none;
}

.collapse-title:hover {
  background: var(--bg-tertiary);
}

.collapse-title svg {
  transition: transform var(--transition-fast);
  color: var(--accent-primary);
}

.collapse[open] .collapse-title svg {
  transform: rotate(90deg);
}

.collapse-content {
  padding: 0 var(--space-lg) var(--space-lg);
  color: var(--text-secondary);
  border-top: 1px solid var(--border-color);
  padding-top: var(--space-md);
}

.collapse-content p:last-child {
  margin-bottom: 0;
}

/* ---------- Layout Improvements ---------- */
/* Match list page width for consistency */
.article {
  max-width: var(--max-width);
}

/* Reduce breadcrumb spacing */
.breadcrumbs {
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-sm);
}

/* Reduce main content top padding */
.main-content {
  padding-top: var(--space-lg);
}

/* Ensure full width containers */
.article-container {
  width: 100%;
}

/* Fix article-content to fill available space */
.article-content {
  max-width: 100%;
}

/* ---------- Newsletter Section ---------- */
.newsletter-section {
  background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-tertiary) 100%);
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
  padding: var(--space-3xl) var(--space-lg);
  margin-top: var(--space-2xl);
}

.newsletter-container {
  max-width: 700px;
  margin: 0 auto;
  text-align: center;
}

.newsletter-content {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.newsletter-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 64px;
  height: 64px;
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  border-radius: 50%;
  color: white;
  margin-bottom: var(--space-sm);
}

.newsletter-title {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--text-primary);
  margin: 0;
}

.newsletter-description {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin: 0;
  max-width: 500px;
}

.newsletter-form {
  position: relative;
}

.form-row {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
  justify-content: center;
  margin-bottom: var(--space-lg);
}

.form-group {
  flex: 1;
  min-width: 180px;
  max-width: 220px;
}

.form-input {
  width: 100%;
  padding: var(--space-md) var(--space-lg);
  font-size: 1rem;
  font-family: var(--font-sans);
  color: var(--text-primary);
  background: var(--bg-primary);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-md);
  transition: border-color var(--transition-base), box-shadow var(--transition-base);
}

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

.form-input:focus {
  outline: none;
  border-color: var(--accent-primary);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.newsletter-btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  font-size: 1rem;
  font-weight: 600;
  font-family: var(--font-sans);
  color: white;
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: transform var(--transition-base), box-shadow var(--transition-base);
  white-space: nowrap;
}

.newsletter-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 20px var(--accent-glow);
}

.newsletter-btn:active {
  transform: translateY(0);
}

.form-consent {
  display: flex;
  justify-content: center;
  margin-bottom: var(--space-lg);
}

.checkbox-label {
  display: flex;
  align-items: flex-start;
  gap: var(--space-sm);
  cursor: pointer;
  text-align: left;
  max-width: 500px;
}

.form-checkbox {
  position: absolute;
  opacity: 0;
  cursor: pointer;
}

.checkmark {
  flex-shrink: 0;
  width: 20px;
  height: 20px;
  background: var(--bg-primary);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
  position: relative;
}

.checkbox-label:hover .checkmark {
  border-color: var(--accent-primary);
}

.form-checkbox:checked + .checkmark {
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  border-color: var(--gradient-start);
}

.form-checkbox:checked + .checkmark::after {
  content: '';
  position: absolute;
  left: 6px;
  top: 2px;
  width: 5px;
  height: 10px;
  border: solid white;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

.form-checkbox:focus + .checkmark {
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.consent-text {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.newsletter-privacy {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-xs);
  font-size: 0.8rem;
  color: var(--text-tertiary);
  margin: 0;
}

.newsletter-privacy a {
  color: var(--accent-primary);
  text-decoration: none;
}

.newsletter-privacy a:hover {
  text-decoration: underline;
}

/* Visually hidden but accessible */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Newsletter responsive */
@media (max-width: 640px) {
  .newsletter-section {
    padding: var(--space-2xl) var(--space-md);
  }

  .newsletter-title {
    font-size: 1.5rem;
  }

  .newsletter-description {
    font-size: 1rem;
  }

  .form-row {
    flex-direction: column;
    align-items: stretch;
  }

  .form-group {
    max-width: 100%;
  }

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

  .checkbox-label {
    max-width: 100%;
  }
}

/* ---------- Search Toggle (Header) ---------- */
.search-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  color: var(--text-secondary);
  background: transparent;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
}

.search-toggle:hover {
  color: var(--text-primary);
  background: var(--bg-tertiary);
}

/* ---------- Search Page ---------- */
.search-page {
  min-height: calc(100vh - var(--header-height) - 200px);
  padding: var(--space-2xl) var(--space-lg);
}

.search-container {
  max-width: 800px;
  margin: 0 auto;
}

.search-title {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--text-primary);
  text-align: center;
  margin-bottom: var(--space-sm);
}

.search-subtitle {
  color: var(--text-secondary);
  text-align: center;
  margin-bottom: var(--space-xl);
}

.search-input-wrapper {
  position: relative;
  display: flex;
  align-items: center;
  background: var(--bg-secondary);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: var(--space-md) var(--space-lg);
  transition: all var(--transition-base);
}

.search-input-wrapper:focus-within {
  border-color: var(--accent-primary);
  box-shadow: 0 0 0 4px var(--accent-glow);
}

.search-input-wrapper svg {
  color: var(--text-muted);
  flex-shrink: 0;
}

.search-input {
  flex: 1;
  border: none;
  background: transparent;
  font-size: 1.125rem;
  font-family: var(--font-sans);
  color: var(--text-primary);
  padding: 0 var(--space-md);
  outline: none;
}

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

.search-clear {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  background: var(--bg-tertiary);
  border: none;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.search-clear:hover {
  background: var(--border-color);
  color: var(--text-primary);
}

.search-filters {
  display: flex;
  gap: var(--space-sm);
  justify-content: center;
  flex-wrap: wrap;
  margin-top: var(--space-lg);
}

.filter-btn {
  padding: var(--space-sm) var(--space-lg);
  font-size: 0.875rem;
  font-weight: 500;
  font-family: var(--font-sans);
  color: var(--text-secondary);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  cursor: pointer;
  transition: all var(--transition-base);
}

.filter-btn:hover {
  color: var(--text-primary);
  border-color: var(--text-muted);
}

.filter-btn.active {
  color: white;
  background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
  border-color: transparent;
}

.search-info {
  text-align: center;
  color: var(--text-secondary);
  margin-top: var(--space-xl);
  font-size: 0.95rem;
}

.search-results {
  margin-top: var(--space-xl);
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.search-result-item {
  display: block;
  padding: var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all var(--transition-base);
}

.search-result-item:hover {
  border-color: var(--accent-primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.result-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-sm);
}

.result-subject {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--subject-color);
  background: color-mix(in srgb, var(--subject-color) 15%, transparent);
  padding: var(--space-xs) var(--space-sm);
  border-radius: var(--radius-sm);
}

.result-title {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--text-primary);
  margin: 0;
}

.result-title mark {
  background: var(--accent-glow);
  color: var(--accent-primary);
  padding: 0 2px;
  border-radius: 2px;
}

.result-snippet {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin: var(--space-sm) 0 0;
}

.result-tags {
  display: flex;
  gap: var(--space-xs);
  flex-wrap: wrap;
  margin-top: var(--space-sm);
}

.result-tag {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  background: var(--bg-tertiary);
  padding: 2px var(--space-sm);
  border-radius: var(--radius-sm);
}

.no-results {
  text-align: center;
  padding: var(--space-2xl);
  color: var(--text-secondary);
}

.no-results p {
  margin: var(--space-sm) 0;
}

/* Search responsive */
@media (max-width: 640px) {
  .search-title {
    font-size: 1.75rem;
  }

  .search-input {
    font-size: 1rem;
  }

  .filter-btn {
    padding: var(--space-xs) var(--space-md);
    font-size: 0.8rem;
  }

  .result-header {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-xs);
  }
}

/* ---------- Details/Summary Block ---------- */
.details-block {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  margin: var(--space-md) 0;
}

.details-summary {
  padding: var(--space-md) var(--space-lg);
  cursor: pointer;
  font-weight: 600;
  color: var(--text-primary);
  list-style: none;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.details-summary::-webkit-details-marker {
  display: none;
}

.details-summary::before {
  content: '▶';
  font-size: 0.75em;
  transition: transform var(--transition-base);
}

.details-block[open] .details-summary::before {
  transform: rotate(90deg);
}

.details-content {
  padding: 0 var(--space-lg) var(--space-lg);
  color: var(--text-secondary);
  border-top: 1px solid var(--border-color);
}

.details-content p:last-child {
  margin-bottom: 0;
}

/* ---------- Print Styles ---------- */
@media print {
  .site-header,
  .site-footer,
  .toc-sidebar,
  .article-nav,
  .theme-toggle,
  .nav-toggle,
  .newsletter-section {
    display: none !important;
  }

  .main-content {
    padding: 0;
  }

  .article {
    max-width: 100%;
  }

  body {
    color: #000;
    background: #fff;
  }
}