/* Math Encyclopedia - Cedar Design System */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500;600&display=swap');

:root {
  /* Cedar Fluid Design System - Yellow-Green Palette */
  --background: #fdffe9;
  --foreground: #2e3105;
  --card: #ffffff;
  --card-foreground: #2e3105;
  --primary: #dee777;
  --primary-foreground: #2e3105;
  --secondary: #f5f7dc;
  --secondary-foreground: #2e3105;
  --muted: #f5f7dc;
  --muted-foreground: #5a5d3a;
  --accent: #dee777;
  --accent-foreground: #2e3105;
  --border: rgba(46, 49, 5, 0.1);
  --border-hover: rgba(46, 49, 5, 0.2);
  --shadow: 0 2px 12px rgba(46, 49, 5, 0.08);
  --shadow-lg: 0 8px 32px rgba(46, 49, 5, 0.12);
  
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  
  /* Layout */
  --max-width: 1200px;
  --header-height: 70px;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 16px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--background);
  color: var(--foreground);
  line-height: 1.6;
  min-height: 100vh;
}

/* Header */
.site-header {
  background: var(--card);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}

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

.logo {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  text-decoration: none;
  color: var(--foreground);
}

.logo-icon {
  width: 40px;
  height: 40px;
  background: var(--primary);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.25rem;
}

.logo-text {
  font-size: 1.25rem;
  font-weight: 700;
}

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

.nav-links a {
  text-decoration: none;
  color: var(--muted-foreground);
  font-weight: 500;
  transition: color 0.2s;
  position: relative;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--foreground);
}

.nav-links a.active::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--primary);
  border-radius: 2px;
}

.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--spacing-sm);
}

/* Main Content */
.main-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--spacing-2xl) var(--spacing-lg);
}

/* Hero Section */
.hero {
  text-align: center;
  padding: var(--spacing-2xl) 0;
  margin-bottom: var(--spacing-2xl);
}

.hero h1 {
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 700;
  margin-bottom: var(--spacing-md);
  line-height: 1.2;
}

.hero p {
  font-size: 1.125rem;
  color: var(--muted-foreground);
  max-width: 600px;
  margin: 0 auto;
}

/* Search Bar */
.search-container {
  max-width: 600px;
  margin: var(--spacing-xl) auto;
  position: relative;
}

.search-input {
  width: 100%;
  padding: var(--spacing-md) var(--spacing-lg);
  padding-left: 3rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  background: var(--card);
  font-size: 1rem;
  color: var(--foreground);
  transition: border-color 0.2s, box-shadow 0.2s;
}

.search-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(222, 231, 119, 0.3);
}

.search-icon {
  position: absolute;
  left: var(--spacing-md);
  top: 50%;
  transform: translateY(-50%);
  color: var(--muted-foreground);
}

/* Tag Cloud */
.tag-cloud {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  justify-content: center;
  margin-bottom: var(--spacing-2xl);
  padding: var(--spacing-lg);
}

.tag {
  display: inline-flex;
  align-items: center;
  padding: var(--spacing-sm) var(--spacing-md);
  background: var(--secondary);
  border-radius: 100px;
  text-decoration: none;
  color: var(--foreground);
  font-weight: 500;
  font-size: 0.875rem;
  transition: all 0.2s;
  border: 1px solid transparent;
}

.tag:hover {
  background: var(--primary);
  transform: translateY(-2px);
}

.tag.active {
  background: var(--primary);
  border-color: var(--foreground);
}

/* Section Title */
.section-title {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: var(--spacing-lg);
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.section-title::before {
  content: '';
  width: 4px;
  height: 28px;
  background: var(--primary);
  border-radius: 2px;
}

/* Topic Grid */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--spacing-xl);
  margin-bottom: var(--spacing-2xl);
}

/* Topic Card */
.topic-card {
  background: var(--card);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform 0.3s, box-shadow 0.3s;
  border: 1px solid var(--border);
  display: flex;
  flex-direction: column;
}

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

.topic-image {
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background: var(--secondary);
  width: 100%;
}

.topic-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.3s;
  display: block;
}

.topic-card:hover .topic-image img {
  transform: scale(1.05);
}

.topic-content {
  padding: var(--spacing-lg);
  flex: 1;
  display: flex;
  flex-direction: column;
}

.topic-content h3 {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
  line-height: 1.3;
}

.topic-content p {
  font-size: 0.875rem;
  color: var(--muted-foreground);
  margin-bottom: var(--spacing-md);
  line-height: 1.5;
  flex: 1;
}

.read-more {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  color: var(--foreground);
  text-decoration: none;
  font-weight: 600;
  font-size: 0.875rem;
  transition: gap 0.2s;
}

.read-more:hover {
  gap: var(--spacing-sm);
}

.read-more::after {
  content: '→';
  transition: transform 0.2s;
}

.read-more:hover::after {
  transform: translateX(4px);
}

/* Category Badge */
.category-badge {
  display: inline-block;
  padding: 2px 8px;
  background: var(--primary);
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

/* Topic Detail Page */
.topic-detail {
  max-width: 800px;
  margin: 0 auto;
  background: var(--card);
  border-radius: var(--radius-lg);
  padding: var(--spacing-2xl);
  box-shadow: var(--shadow);
}

.topic-header {
  border-bottom: 2px solid var(--primary);
  padding-bottom: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

.topic-header h1 {
  font-size: 2.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  line-height: 1.2;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 0.875rem;
  color: var(--muted-foreground);
  margin-bottom: var(--spacing-md);
}

.breadcrumb a {
  color: var(--muted-foreground);
  text-decoration: none;
}

.breadcrumb a:hover {
  color: var(--foreground);
}

/* Content Sections */
.content-section {
  margin-bottom: var(--spacing-xl);
}

.content-section h2 {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
  padding-left: var(--spacing-md);
  border-left: 4px solid var(--primary);
}

.content-section p {
  margin-bottom: var(--spacing-md);
  line-height: 1.8;
}

.content-section ul,
.content-section ol {
  margin-left: var(--spacing-lg);
  margin-bottom: var(--spacing-md);
}

.content-section li {
  margin-bottom: var(--spacing-sm);
}

/* Formula Box */
.formula-box {
  background: var(--secondary);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin: var(--spacing-md) 0;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 1.25rem;
  border-left: 4px solid var(--primary);
}

/* Example Box */
.example-box {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin: var(--spacing-md) 0;
}

.example-box .question {
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

.example-box .solution {
  color: var(--muted-foreground);
  padding-left: var(--spacing-md);
  border-left: 2px solid var(--primary);
}

/* Related Topics */
.related-topics {
  background: var(--secondary);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin-top: var(--spacing-xl);
}

.related-topics h3 {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
}

.related-topics ul {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
}

.related-topics li a {
  display: inline-block;
  padding: var(--spacing-xs) var(--spacing-md);
  background: var(--card);
  border-radius: 100px;
  text-decoration: none;
  color: var(--foreground);
  font-size: 0.875rem;
  transition: background 0.2s;
}

.related-topics li a:hover {
  background: var(--primary);
}

/* Footer */
.site-footer {
  background: var(--foreground);
  color: var(--background);
  padding: var(--spacing-2xl) 0;
  margin-top: var(--spacing-2xl);
}

.footer-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--spacing-xl);
}

.footer-section h4 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
  color: var(--primary);
}

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

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

.footer-section a {
  color: var(--muted-foreground);
  text-decoration: none;
  font-size: 0.875rem;
  transition: color 0.2s;
}

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

.footer-bottom {
  max-width: var(--max-width);
  margin: var(--spacing-xl) auto 0;
  padding: var(--spacing-lg) var(--spacing-lg) 0;
  border-top: 1px solid rgba(253, 255, 233, 0.1);
  text-align: center;
  font-size: 0.875rem;
  color: var(--muted-foreground);
}

/* Responsive Design */
@media (max-width: 768px) {
  :root {
    --header-height: 60px;
  }

  body {
    padding-top: 56px; /* compensate fixed academic-nav-widget */
  }

  .nav-links {
    display: none;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: var(--card);
    flex-direction: column;
    padding: var(--spacing-md);
    gap: var(--spacing-md);
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow);
  }
  
  .nav-links.active {
    display: flex;
  }
  
  .mobile-menu-btn {
    display: block;
  }

  .main-container {
    padding: var(--spacing-md);
  }
  
  .topic-grid,
  .topics-grid {
    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
    gap: var(--spacing-md);
  }
  
  .hero h1 {
    font-size: 1.75rem;
  }
  
  .topic-detail {
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
  }
  
  .topic-header h1 {
    font-size: 1.75rem;
  }

  .category-header {
    padding: var(--spacing-lg) var(--spacing-md);
  }

  .footer-content {
    padding: 0 var(--spacing-md);
  }
}

@media (max-width: 480px) {
  body {
    padding-top: 52px;
  }

  .main-container {
    padding: var(--spacing-sm) var(--spacing-md);
  }
  
  .topic-grid,
  .topics-grid {
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-sm);
  }
  
  .tag-cloud {
    padding: var(--spacing-sm) var(--spacing-md);
  }
  
  .footer-container {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .topic-content {
    padding: var(--spacing-sm);
  }

  .formula-box {
    font-size: 1rem;
    padding: var(--spacing-md);
  }
}

/* Utility Classes */
.text-center { text-align: center; }
.text-muted { color: var(--muted-foreground); }
.hidden { display: none !important; }
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

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

.fade-in {
  animation: fadeIn 0.4s ease-out;
}

/* Print Styles */
@media print {
  .site-header,
  .site-footer,
  .tag-cloud,
  .search-container {
    display: none;
  }
  
  .topic-detail {
    box-shadow: none;
  }
}

/* Accordion expand for topic cards */
.topic-expand {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease;
  font-size: 0.875rem;
  color: var(--muted-foreground);
  line-height: 1.6;
}

.topic-card.expanded .topic-expand {
  max-height: 400px;
}

.read-more-toggle {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  color: var(--foreground);
  background: none;
  border: none;
  padding: 0;
  font-weight: 600;
  font-size: 0.875rem;
  cursor: pointer;
  transition: gap 0.2s;
}

.read-more-toggle::after {
  content: '↓';
  transition: transform 0.3s;
}

.topic-card.expanded .read-more-toggle::after {
  transform: rotate(180deg);
}