/* ==========================================================================
   WOKDEX Corpus — Design System
   Scientific Repository for Formative Assessment Research
   ========================================================================== */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* --- CSS Custom Properties (Design Tokens) --- */
/* Light theme (default) */
:root {
  /* Background */
  --bg-primary: #f8fafc;
  --bg-secondary: #f1f5f9;
  --bg-card: #ffffff;
  --bg-card-hover: #f0f7ff;
  --bg-surface: #e8f0fe;
  --bg-glass: rgba(255, 255, 255, 0.75);

  /* Accent Colors */
  --accent-cyan: #0891b2;
  --accent-cyan-glow: rgba(8, 145, 178, 0.15);
  --accent-orange: #ea6c00;
  --accent-orange-glow: rgba(234, 108, 0, 0.15);
  --accent-green: #16a34a;
  --accent-green-glow: rgba(22, 163, 74, 0.15);
  --accent-red: #dc2626;
  --accent-red-glow: rgba(220, 38, 38, 0.15);
  --accent-purple: #9333ea;
  --accent-purple-glow: rgba(147, 51, 234, 0.15);
  --accent-blue: #2563eb;
  --accent-yellow: #ca8a04;

  /* Text */
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --text-accent: #0891b2;

  /* Borders */
  --border-subtle: rgba(15, 23, 42, 0.08);
  --border-medium: rgba(15, 23, 42, 0.15);
  --border-accent: rgba(8, 145, 178, 0.35);

  /* Gradients */
  --gradient-hero: linear-gradient(135deg, #f0f7ff 0%, #e8f4fd 40%, #eef2ff 100%);
  --gradient-card: linear-gradient(135deg, rgba(255,255,255,0.95), rgba(248,250,252,0.9));
  --gradient-accent: linear-gradient(135deg, #0891b2, #2563eb);
  --gradient-warm: linear-gradient(135deg, #f97316, #ef4444);
  --gradient-success: linear-gradient(135deg, #16a34a, #0891b2);

  /* 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;
  --space-4xl: 6rem;

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-pill: 100px;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(15, 23, 42, 0.08);
  --shadow-md: 0 4px 16px rgba(15, 23, 42, 0.12);
  --shadow-lg: 0 8px 32px rgba(15, 23, 42, 0.16);
  --shadow-glow-cyan: 0 0 20px rgba(8, 145, 178, 0.15);
  --shadow-glow-orange: 0 0 20px rgba(234, 108, 0, 0.15);

  /* Typography */
  --font-body: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);

  /* Layout */
  --max-width: 1280px;
  --nav-height: 64px;

  /* Nav background (theme-specific) */
  --nav-bg: rgba(248, 250, 252, 0.88);
  --nav-mobile-bg: rgba(248, 250, 252, 0.97);
}

/* Dark theme override */
[data-theme="dark"] {
  /* Background */
  --bg-primary: #0a0e1a;
  --bg-secondary: #111827;
  --bg-card: #1a1f35;
  --bg-card-hover: #222845;
  --bg-surface: #161b2e;
  --bg-glass: rgba(26, 31, 53, 0.7);

  /* Accent Colors */
  --accent-cyan: #06b6d4;
  --accent-cyan-glow: rgba(6, 182, 212, 0.25);
  --accent-orange: #f97316;
  --accent-orange-glow: rgba(249, 115, 22, 0.25);
  --accent-green: #22c55e;
  --accent-green-glow: rgba(34, 197, 94, 0.25);
  --accent-red: #ef4444;
  --accent-red-glow: rgba(239, 68, 68, 0.25);
  --accent-purple: #a855f7;
  --accent-purple-glow: rgba(168, 85, 247, 0.25);
  --accent-blue: #3b82f6;
  --accent-yellow: #eab308;

  /* Text */
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --text-accent: #06b6d4;

  /* Borders */
  --border-subtle: rgba(148, 163, 184, 0.1);
  --border-medium: rgba(148, 163, 184, 0.2);
  --border-accent: rgba(6, 182, 212, 0.3);

  /* Gradients */
  --gradient-hero: linear-gradient(135deg, #0a0e1a 0%, #111827 40%, #0f1629 100%);
  --gradient-card: linear-gradient(135deg, rgba(26, 31, 53, 0.9), rgba(22, 27, 46, 0.7));
  --gradient-accent: linear-gradient(135deg, #06b6d4, #3b82f6);
  --gradient-warm: linear-gradient(135deg, #f97316, #ef4444);
  --gradient-success: linear-gradient(135deg, #22c55e, #06b6d4);

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
  --shadow-glow-cyan: 0 0 20px rgba(6, 182, 212, 0.15);
  --shadow-glow-orange: 0 0 20px rgba(249, 115, 22, 0.15);

  /* Nav background (theme-specific) */
  --nav-bg: rgba(10, 14, 26, 0.85);
  --nav-mobile-bg: rgba(10, 14, 26, 0.95);
}

/* Auto dark theme based on system preference (no JS needed for initial load) */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    /* Background */
    --bg-primary: #0a0e1a;
    --bg-secondary: #111827;
    --bg-card: #1a1f35;
    --bg-card-hover: #222845;
    --bg-surface: #161b2e;
    --bg-glass: rgba(26, 31, 53, 0.7);

    /* Accent Colors */
    --accent-cyan: #06b6d4;
    --accent-cyan-glow: rgba(6, 182, 212, 0.25);
    --accent-orange: #f97316;
    --accent-orange-glow: rgba(249, 115, 22, 0.25);
    --accent-green: #22c55e;
    --accent-green-glow: rgba(34, 197, 94, 0.25);
    --accent-red: #ef4444;
    --accent-red-glow: rgba(239, 68, 68, 0.25);
    --accent-purple: #a855f7;
    --accent-purple-glow: rgba(168, 85, 247, 0.25);
    --accent-blue: #3b82f6;
    --accent-yellow: #eab308;

    /* Text */
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    --text-accent: #06b6d4;

    /* Borders */
    --border-subtle: rgba(148, 163, 184, 0.1);
    --border-medium: rgba(148, 163, 184, 0.2);
    --border-accent: rgba(6, 182, 212, 0.3);

    /* Gradients */
    --gradient-hero: linear-gradient(135deg, #0a0e1a 0%, #111827 40%, #0f1629 100%);
    --gradient-card: linear-gradient(135deg, rgba(26, 31, 53, 0.9), rgba(22, 27, 46, 0.7));
    --gradient-accent: linear-gradient(135deg, #06b6d4, #3b82f6);
    --gradient-warm: linear-gradient(135deg, #f97316, #ef4444);
    --gradient-success: linear-gradient(135deg, #22c55e, #06b6d4);

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    --shadow-glow-cyan: 0 0 20px rgba(6, 182, 212, 0.15);
    --shadow-glow-orange: 0 0 20px rgba(249, 115, 22, 0.15);

    /* Nav background */
    --nav-bg: rgba(10, 14, 26, 0.85);
    --nav-mobile-bg: rgba(10, 14, 26, 0.95);
  }
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  min-height: 100vh;
  overflow-x: hidden;
}

/* --- Typography --- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

h1 { font-size: clamp(2rem, 5vw, 3.25rem); }
h2 { font-size: clamp(1.5rem, 3.5vw, 2.25rem); }
h3 { font-size: clamp(1.15rem, 2.5vw, 1.5rem); }
h4 { font-size: 1.125rem; }

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

a {
  color: var(--accent-cyan);
  text-decoration: none;
  transition: color var(--transition-fast);
}
a:hover { color: #22d3ee; }

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

code {
  background: rgba(6, 182, 212, 0.1);
  color: var(--accent-cyan);
  padding: 0.15em 0.4em;
  border-radius: var(--radius-sm);
  font-size: 0.875em;
}

pre {
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  overflow-x: auto;
  font-size: 0.85rem;
  line-height: 1.6;
}

pre code {
  background: none;
  padding: 0;
  color: var(--text-primary);
}

/* --- Layout --- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl);
}

.section {
  padding: var(--space-4xl) 0;
}

.section-header {
  text-align: center;
  margin-bottom: var(--space-3xl);
}

.section-header h2 {
  margin-bottom: var(--space-md);
}

.section-header p {
  max-width: 680px;
  margin: 0 auto;
  font-size: 1.1rem;
}

.section-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent-cyan);
  background: var(--accent-cyan-glow);
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--radius-pill);
  margin-bottom: var(--space-md);
}

/* --- Navigation --- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--nav-bg);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border-bottom: 1px solid var(--border-subtle);
  z-index: 1000;
  transition: background var(--transition-base);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl);
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 800;
  font-size: 1.25rem;
  color: var(--text-primary);
  text-decoration: none;
}

.nav-logo .logo-icon {
  width: 32px;
  height: 32px;
  background: var(--gradient-accent);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
}

.nav-logo span.accent { color: var(--accent-cyan); }

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

.nav-links a {
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  padding: var(--space-xs) var(--space-sm);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--text-primary);
  background: rgba(148, 163, 184, 0.08);
}

.nav-links a.active {
  color: var(--accent-cyan);
}

.nav-hamburger {
  display: none;
  cursor: pointer;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  padding: var(--space-sm);
}

.nav-hamburger span {
  width: 22px;
  height: 2px;
  background: var(--text-primary);
  border-radius: 2px;
  transition: all var(--transition-fast);
}

/* --- Hero Section --- */
.hero {
  padding-top: calc(var(--nav-height) + var(--space-4xl));
  padding-bottom: var(--space-4xl);
  background: var(--gradient-hero);
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(6, 182, 212, 0.08), transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.hero::after {
  content: '';
  position: absolute;
  bottom: -30%;
  left: -10%;
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(59, 130, 246, 0.06), transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 820px;
  margin: 0 auto;
  text-align: center;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  background: rgba(6, 182, 212, 0.1);
  border: 1px solid rgba(6, 182, 212, 0.2);
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--radius-pill);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-cyan);
  margin-bottom: var(--space-xl);
  animation: fadeInUp 0.6s ease both;
}

.hero-badge .dot {
  width: 8px;
  height: 8px;
  background: var(--accent-green);
  border-radius: 50%;
  animation: pulse-dot 2s ease infinite;
}

@keyframes pulse-dot {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.5; transform: scale(1.3); }
}

.hero h1 {
  margin-bottom: var(--space-lg);
  animation: fadeInUp 0.6s 0.1s ease both;
}

.hero h1 .highlight {
  background: var(--gradient-accent);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-subtitle {
  font-size: 1.15rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-2xl);
  line-height: 1.8;
  animation: fadeInUp 0.6s 0.2s ease both;
}

.hero-actions {
  display: flex;
  gap: var(--space-md);
  justify-content: center;
  flex-wrap: wrap;
  animation: fadeInUp 0.6s 0.3s ease both;
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 0.75rem 1.5rem;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  font-weight: 600;
  font-family: var(--font-body);
  cursor: pointer;
  border: none;
  transition: all var(--transition-base);
  text-decoration: none;
}

.btn-primary {
  background: var(--gradient-accent);
  color: white;
  box-shadow: 0 4px 15px rgba(6, 182, 212, 0.3);
}
.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgba(6, 182, 212, 0.4);
  color: white;
}

.btn-secondary {
  background: rgba(148, 163, 184, 0.08);
  color: var(--text-primary);
  border: 1px solid var(--border-medium);
}
.btn-secondary:hover {
  background: rgba(148, 163, 184, 0.15);
  border-color: var(--border-accent);
  color: var(--text-primary);
}

/* --- Stat Cards --- */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--space-lg);
}

.stat-card {
  background: var(--gradient-card);
  backdrop-filter: blur(12px);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  text-align: center;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

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

.stat-card:hover {
  transform: translateY(-4px);
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow-cyan);
}

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

.stat-card .stat-value {
  font-size: 2.5rem;
  font-weight: 800;
  background: var(--gradient-accent);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.2;
}

.stat-card .stat-label {
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-top: var(--space-xs);
  font-weight: 500;
}

.stat-card .stat-icon {
  font-size: 1.5rem;
  margin-bottom: var(--space-sm);
}

/* --- Cards Grid --- */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: var(--space-lg);
}

.exercise-card {
  background: var(--gradient-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: all var(--transition-base);
  cursor: pointer;
  position: relative;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  display: block;
}

.exercise-card:hover {
  transform: translateY(-4px);
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow-cyan);
  color: inherit;
}

.exercise-card .card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: var(--space-md);
  margin-bottom: var(--space-md);
}

.exercise-card .card-id {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
}

.exercise-card .card-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-xs);
}

.exercise-card .card-overview {
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
  line-height: 1.6;
}

.exercise-card .card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
}

.exercise-card .card-stats {
  display: flex;
  justify-content: space-between;
  padding-top: var(--space-md);
  border-top: 1px solid var(--border-subtle);
  font-size: 0.8rem;
  color: var(--text-muted);
}

.exercise-card .card-stats span {
  display: flex;
  align-items: center;
  gap: 4px;
}

/* --- Badges --- */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  white-space: nowrap;
}

.badge-tdd {
  background: var(--accent-green-glow);
  color: var(--accent-green);
  border: 1px solid rgba(34, 197, 94, 0.3);
}

.badge-false-green {
  background: var(--accent-orange-glow);
  color: var(--accent-orange);
  border: 1px solid rgba(249, 115, 22, 0.3);
}

.badge-performance {
  background: var(--accent-red-glow);
  color: var(--accent-red);
  border: 1px solid rgba(239, 68, 68, 0.3);
}

.badge-sample {
  background: var(--accent-purple-glow);
  color: var(--accent-purple);
  border: 1px solid rgba(168, 85, 247, 0.3);
}

.badge-difficulty {
  font-family: var(--font-mono);
  font-weight: 700;
  min-width: 28px;
  text-align: center;
  justify-content: center;
}

.badge-diff-E { background: rgba(34, 197, 94, 0.15); color: #4ade80; border: 1px solid rgba(34, 197, 94, 0.3); }
.badge-diff-D { background: rgba(59, 130, 246, 0.15); color: #60a5fa; border: 1px solid rgba(59, 130, 246, 0.3); }
.badge-diff-C { background: rgba(234, 179, 8, 0.15); color: #facc15; border: 1px solid rgba(234, 179, 8, 0.3); }
.badge-diff-B { background: rgba(249, 115, 22, 0.15); color: #fb923c; border: 1px solid rgba(249, 115, 22, 0.3); }
.badge-diff-A { background: rgba(239, 68, 68, 0.15); color: #f87171; border: 1px solid rgba(239, 68, 68, 0.3); }

.badge-skill {
  background: rgba(148, 163, 184, 0.08);
  color: var(--text-secondary);
  border: 1px solid var(--border-subtle);
  font-size: 0.7rem;
  text-transform: none;
  font-weight: 500;
}

.badge-cs {
  background: rgba(6, 182, 212, 0.1);
  color: var(--accent-cyan);
  border: 1px solid rgba(6, 182, 212, 0.2);
}

/* --- Tables --- */
.table-wrapper {
  overflow-x: auto;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-subtle);
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
}

thead {
  background: var(--bg-surface);
}

th {
  padding: var(--space-md) var(--space-lg);
  text-align: left;
  font-weight: 600;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  border-bottom: 1px solid var(--border-medium);
  white-space: nowrap;
}

td {
  padding: var(--space-md) var(--space-lg);
  border-bottom: 1px solid var(--border-subtle);
  color: var(--text-secondary);
}

tbody tr {
  transition: background var(--transition-fast);
}

tbody tr:hover {
  background: rgba(148, 163, 184, 0.04);
}

tbody tr:last-child td {
  border-bottom: none;
}

/* --- Charts --- */
.chart-container {
  background: var(--gradient-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
}

.chart-title {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: var(--space-lg);
  color: var(--text-primary);
}

.charts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: var(--space-lg);
}

/* --- Filters --- */
.filters {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
  align-items: center;
}

.filter-group {
  display: flex;
  gap: var(--space-xs);
  flex-wrap: wrap;
}

.filter-btn {
  padding: var(--space-xs) var(--space-md);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-pill);
  background: transparent;
  color: var(--text-secondary);
  font-size: 0.8rem;
  font-weight: 500;
  font-family: var(--font-body);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.filter-btn:hover {
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
}

.filter-btn.active {
  background: rgba(6, 182, 212, 0.15);
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
}

.search-input {
  flex: 1;
  min-width: 240px;
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-card);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.9rem;
  font-family: var(--font-body);
  transition: border-color var(--transition-fast);
}

.search-input::placeholder { color: var(--text-muted); }
.search-input:focus {
  outline: none;
  border-color: var(--accent-cyan);
  box-shadow: 0 0 0 3px var(--accent-cyan-glow);
}

/* --- Contributions --- */
.contributions-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-lg);
}

.contrib-card {
  background: var(--gradient-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: all var(--transition-base);
  position: relative;
}

.contrib-card:hover {
  border-color: var(--border-accent);
  transform: translateY(-2px);
}

.contrib-card .contrib-id {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--accent-cyan);
  margin-bottom: var(--space-sm);
}

.contrib-card h3 {
  font-size: 1.05rem;
  margin-bottom: var(--space-sm);
}

.contrib-card p {
  font-size: 0.85rem;
  line-height: 1.6;
}

/* --- Footer --- */
.footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  padding: var(--space-3xl) 0;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-lg);
}

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

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

.footer-links a {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

/* --- Detail Page --- */
.detail-header {
  padding-top: calc(var(--nav-height) + var(--space-3xl));
  padding-bottom: var(--space-2xl);
  background: var(--gradient-hero);
}

.detail-breadcrumb {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: var(--space-lg);
}

.detail-breadcrumb a { color: var(--text-secondary); }

.detail-title-row {
  display: flex;
  align-items: flex-start;
  gap: var(--space-lg);
  flex-wrap: wrap;
}

.detail-badges {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
  margin-top: var(--space-md);
}

.detail-meta-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: var(--space-md);
  margin-top: var(--space-xl);
}

.detail-meta-item {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: var(--space-md);
}

.detail-meta-item .meta-label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 2px;
}

.detail-meta-item .meta-value {
  font-weight: 600;
  font-size: 1rem;
  color: var(--text-primary);
}

.detail-editorial {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-xl);
}

.detail-editorial h3 {
  margin-bottom: var(--space-md);
}

.detail-editorial p {
  line-height: 1.8;
}

.help-tip-text {
  font-style: italic;
  color: var(--accent-orange);
  font-size: 0.85rem;
}

/* --- Animations --- */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

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

.animate-in {
  animation: fadeInUp 0.5s ease both;
}

.animate-in-delay-1 { animation-delay: 0.1s; }
.animate-in-delay-2 { animation-delay: 0.2s; }
.animate-in-delay-3 { animation-delay: 0.3s; }
.animate-in-delay-4 { animation-delay: 0.4s; }

/* --- Loading --- */
.loading {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-4xl);
}

.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border-subtle);
  border-top-color: var(--accent-cyan);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* --- Empty State --- */
.empty-state {
  text-align: center;
  padding: var(--space-4xl);
  color: var(--text-muted);
}

.empty-state .empty-icon {
  font-size: 3rem;
  margin-bottom: var(--space-md);
}

/* --- Responsive --- */
@media (max-width: 768px) {
  .container { padding: 0 var(--space-md); }

  .nav-links { display: none; }
  .nav-hamburger { display: flex; }

  .nav-links.open {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--nav-mobile-bg);
    backdrop-filter: blur(20px);
    padding: var(--space-lg);
    border-bottom: 1px solid var(--border-subtle);
  }

  .hero { padding-top: calc(var(--nav-height) + var(--space-2xl)); }

  .cards-grid { grid-template-columns: 1fr; }
  .charts-grid { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .contributions-grid { grid-template-columns: 1fr; }

  .hero-actions { flex-direction: column; align-items: center; }

  .filters { flex-direction: column; }

  .footer-content { flex-direction: column; text-align: center; }
}

@media (max-width: 480px) {
  .stats-grid { grid-template-columns: 1fr; }
}

/* --- Theme Toggle Button --- */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--border-medium);
  background: transparent;
  cursor: pointer;
  font-size: 1rem;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
  margin-left: var(--space-sm);
  flex-shrink: 0;
}

.theme-toggle:hover {
  background: var(--accent-cyan-glow);
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
  transform: scale(1.1);
}

/* Icons: moon shown in light mode, sun shown in dark mode */
.theme-toggle .icon-sun { display: none; }
.theme-toggle .icon-moon { display: inline; }

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

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .theme-toggle .icon-sun { display: inline; }
  :root:not([data-theme="light"]) .theme-toggle .icon-moon { display: none; }
}

/* Smooth transitions for theme switch */
body, .nav, .footer, .stat-card, .exercise-card, .contrib-card,
.chart-container, .detail-editorial, .detail-meta-item, .search-input,
.filter-btn, .btn-secondary, pre, code, td, th, thead {
  transition-property: background, background-color, border-color, color, box-shadow;
  transition-duration: 250ms;
  transition-timing-function: ease;
}

/* --- Slug tag (skills page) --- */
.slug-tag {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.72em;
  padding: 2px 7px;
  border-radius: var(--radius-sm);
  background: rgba(6, 182, 212, 0.08);
  color: var(--accent-cyan);
  border: 1px solid rgba(6, 182, 212, 0.2);
  transition: background var(--transition-fast), color var(--transition-fast);
  user-select: all;
}
.slug-tag:hover {
  background: rgba(6, 182, 212, 0.18);
}