/**
 * GCSE Computer Science Revision Portal - Shared Design System
 * Extracted from GCSE Sort Lab aesthetic
 * Vanilla CSS - Zero build steps required
 */

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

:root {
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;

  /* Clean Modern Education Theme (Default: Crisp, Legible, Friendly) */
  --bg-root: #f8fafc;              /* Slate 50 */
  --bg-surface: #ffffff;           /* Clean white card */
  --bg-surface-elevated: #f1f5f9;  /* Slate 100 */
  --bg-surface-hover: #f8fafc;     /* Card hover */
  --bg-glass: rgba(255, 255, 255, 0.95);
  --border-glass: rgba(0, 0, 0, 0.08);

  /* Border Colors - Subtle, clean 1px borders */
  --border-color: #e2e8f0;         /* Slate 200 */
  --border-hover: #cbd5e1;         /* Slate 300 */
  --border-subtle: #f1f5f9;

  /* Text Colors - High contrast, easy to read */
  --text-primary: #0f172a;         /* Slate 900 */
  --text-secondary: #475569;       /* Slate 600 */
  --text-muted: #64748b;           /* Slate 500 */
  --text-inverse: #ffffff;

  /* Accents - Friendly educational palette */
  --accent-primary: #3b82f6;       /* Blue 500 */
  --accent-primary-hover: #2563eb; /* Blue 600 */
  --accent-violet: #6366f1;        /* Indigo 500 */
  --accent-purple: #8b5cf6;        /* Purple 500 */
  --accent-pink: #ec4899;          /* Pink 500 */
  --accent-cyan: #0284c7;          /* Sky 600 */
  --gradient-brand: linear-gradient(135deg, #4f46e5 0%, #3b82f6 50%, #06b6d4 100%);

  /* Soft Accent Backgrounds */
  --accent-soft-bg: rgba(59, 130, 246, 0.08);
  --accent-soft-border: rgba(59, 130, 246, 0.22);
  --accent-soft-text: #1d4ed8;

  /* Simple clean shadows instead of neon glows */
  --glow-accent: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
  --glow-intense: 0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
  --glow-cyan: 0 2px 4px rgba(2, 132, 199, 0.12);

  /* Status Colors */
  --color-success: #10b981;
  --bg-success-soft: rgba(16, 185, 129, 0.1);
  --border-success: rgba(16, 185, 129, 0.25);
  --text-success: #059669;
  --glow-success: 0 1px 3px rgba(16, 185, 129, 0.15);

  --color-warning: #f59e0b;
  --bg-warning-soft: rgba(245, 158, 11, 0.1);
  --border-warning: rgba(245, 158, 11, 0.25);
  --text-warning: #d97706;

  /* Tag Colors */
  --tag-paper1-bg: #eff6ff;
  --tag-paper1-border: #bfdbfe;
  --tag-paper1-text: #1d4ed8;

  --tag-paper2-bg: #faf5ff;
  --tag-paper2-border: #e9d5ff;
  --tag-paper2-text: #7e22ce;

  --tag-spec-bg: #f1f5f9;
  --tag-spec-border: #cbd5e1;
  --tag-spec-text: #334155;

  /* Crisp, clean corners (no excessive 20px bubble cards) */
  --radius-sm: 6px;
  --radius-md: 8px;
  --radius-lg: 10px;
  --radius-xl: 12px;
  --radius-full: 9999px;

  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 200ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 300ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* Optional Dark Theme */
html.dark {
  --bg-root: #0f172a;
  --bg-surface: #1e293b;
  --bg-surface-elevated: #334155;
  --bg-surface-hover: #334155;
  --bg-glass: rgba(30, 41, 59, 0.95);
  --border-glass: rgba(255, 255, 255, 0.08);

  --border-color: #334155;
  --border-hover: #475569;
  --border-subtle: #1e293b;

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-inverse: #0f172a;

  --accent-soft-bg: rgba(59, 130, 246, 0.15);
  --accent-soft-border: rgba(59, 130, 246, 0.3);
  --accent-soft-text: #93c5fd;

  --tag-paper1-bg: rgba(59, 130, 246, 0.15);
  --tag-paper1-border: rgba(59, 130, 246, 0.3);
  --tag-paper1-text: #93c5fd;

  --tag-paper2-bg: rgba(168, 85, 247, 0.15);
  --tag-paper2-border: rgba(168, 85, 247, 0.3);
  --tag-paper2-text: #d8b4fe;

  --tag-spec-bg: rgba(255, 255, 255, 0.08);
  --tag-spec-border: rgba(255, 255, 255, 0.15);
  --tag-spec-text: #e2e8f0;

  --text-success: #34d399;
  --text-warning: #fbbf24;
}

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

body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  background-color: var(--bg-root);
  color: var(--text-primary);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  line-height: 1.5;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

/* Custom Scrollbars */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: rgba(148, 163, 184, 0.3);
  border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(148, 163, 184, 0.55);
}

/* Background Subtle Styling */
.bg-grid-ambient {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background-color: var(--bg-root);
}

/* Container */
.container {
  width: 100%;
  max-width: 1240px;
  margin-left: auto;
  margin-right: auto;
  padding-left: 20px;
  padding-right: 20px;
  position: relative;
  z-index: 1;
}

/* Badges */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  border-radius: var(--radius-full);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.02em;
  text-transform: uppercase;
  line-height: 1;
  white-space: nowrap;
}

.badge-spec {
  background: var(--tag-spec-bg);
  color: var(--tag-spec-text);
  border: 1px solid var(--tag-spec-border);
}

.badge-paper1 {
  background: var(--tag-paper1-bg);
  color: var(--tag-paper1-text);
  border: 1px solid var(--tag-paper1-border);
}

.badge-paper2 {
  background: var(--tag-paper2-bg);
  color: var(--tag-paper2-text);
  border: 1px solid var(--tag-paper2-border);
}

.badge-live {
  background: var(--bg-success-soft);
  color: var(--text-success);
  border: 1px solid var(--border-success);
  box-shadow: 0 0 10px rgba(16, 185, 129, 0.15);
}

.badge-soon {
  background: rgba(148, 163, 184, 0.1);
  color: var(--text-secondary);
  border: 1px solid rgba(148, 163, 184, 0.2);
}

.badge-topic {
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
  font-family: var(--font-mono);
  font-size: 10.5px;
  font-weight: 600;
  text-transform: none;
}

/* Pulsing Status Dot */
.status-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background-color: var(--color-success);
  position: relative;
}

.status-dot::after {
  content: '';
  position: absolute;
  inset: -2px;
  border-radius: 50%;
  background-color: var(--color-success);
  opacity: 0.6;
  animation: pulseDot 2s infinite ease-out;
}

@keyframes pulseDot {
  0% { transform: scale(1); opacity: 0.8; }
  100% { transform: scale(2.4); opacity: 0; }
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 18px;
  border-radius: var(--radius-md);
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  border: 1px solid transparent;
  line-height: 1;
}

.btn-primary {
  background: var(--accent-primary);
  color: #ffffff;
  box-shadow: 0 2px 10px rgba(99, 102, 241, 0.35);
}

.btn-primary:hover {
  background: var(--accent-primary-hover);
  box-shadow: var(--glow-accent);
  transform: translateY(-1px);
}

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

.btn-secondary {
  background: var(--bg-surface-elevated);
  border-color: var(--border-color);
  color: var(--text-primary);
}

.btn-secondary:hover {
  background: var(--bg-surface-hover);
  border-color: var(--border-hover);
  color: #ffffff;
}

.btn-disabled {
  background: rgba(30, 41, 59, 0.4);
  border-color: var(--border-color);
  color: var(--text-muted);
  cursor: not-allowed;
  pointer-events: none;
}

/* Card Components */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}

@media (min-width: 1024px) {
  .card-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 640px) {
  .nav-badge-spec {
    display: none !important;
  }
  .card-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }
  .module-card {
    padding: 16px;
  }
  .card-header {
    gap: 12px;
    margin-bottom: 12px;
  }
  .card-icon-wrapper {
    width: 42px;
    height: 42px;
  }
  .card-title {
    font-size: 16.5px;
  }
  .card-description {
    margin-bottom: 12px;
    font-size: 13px;
    line-height: 1.5;
  }
  .card-highlights {
    display: none !important;
  }
  .card-tags {
    margin-bottom: 14px;
    gap: 6px;
  }
  .hero-section {
    padding: 24px 0 16px 0 !important;
  }
  .hero-title {
    font-size: 28px !important;
    margin-bottom: 10px !important;
  }
  .hero-subtitle {
    font-size: 13.5px !important;
    margin-bottom: 16px !important;
  }
  .spec-pills {
    margin-bottom: 20px !important;
  }
}

/* Reusable Collapsible Plain English Cards */
details.explainer-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-left: 4px solid var(--accent-primary);
  border-radius: var(--radius-md);
  margin-bottom: 20px;
  overflow: hidden;
  transition: all var(--transition-fast);
}

details.explainer-card summary {
  padding: 12px 16px;
  font-size: 13.5px;
  font-weight: 700;
  color: var(--text-primary);
  cursor: pointer;
  user-select: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  list-style: none;
}

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

details.explainer-card summary .summary-left {
  display: flex;
  align-items: center;
  gap: 8px;
}

details.explainer-card summary .summary-toggle-pill {
  font-size: 11px;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: var(--radius-sm);
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
}

details.explainer-card[open] summary .summary-toggle-pill::after {
  content: 'Hide';
}

details.explainer-card:not([open]) summary .summary-toggle-pill::after {
  content: 'Tap to read';
}

details.explainer-card .explainer-content {
  padding: 0 16px 16px 16px;
  border-top: 1px solid var(--border-color);
  padding-top: 12px;
}

.module-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  padding: 24px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
  overflow: hidden;
  transition: all var(--transition-normal);
  backdrop-filter: blur(12px);
}

.module-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: transparent;
  transition: background var(--transition-normal);
}

.module-card.active {
  border-color: var(--border-color);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.05);
}

.module-card.active::before {
  background: var(--accent-primary);
}

.module-card.active:hover {
  border-color: var(--accent-primary);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
  transform: translateY(-2px);
}

.module-card.placeholder {
  opacity: 0.85;
  background: var(--bg-surface-elevated);
  border-style: dashed;
}

.module-card.placeholder:hover {
  opacity: 1;
  border-color: var(--border-hover);
  background: var(--bg-surface);
  transform: translateY(-2px);
}

/* Card Header */
.card-header {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 16px;
}

.card-header-text {
  display: flex;
  flex-direction: column;
  gap: 3px;
  min-width: 0;
  flex: 1;
}

.card-section-tag {
  font-size: 11px;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  line-height: 1;
}

.card-title {
  font-size: 18px;
  font-weight: 800;
  letter-spacing: -0.02em;
  margin: 0;
  color: var(--text-primary);
  line-height: 1.25;
}

.card-icon-wrapper {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: transform var(--transition-fast);
}

.module-card:hover .card-icon-wrapper {
  transform: scale(1.05);
}

.card-icon-active {
  background: var(--gradient-brand);
  color: #ffffff;
  box-shadow: 0 4px 14px rgba(99, 102, 241, 0.4);
}

.card-icon-placeholder {
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
}

.card-description {
  font-size: 13.5px;
  color: var(--text-secondary);
  line-height: 1.6;
  margin: 0 0 20px 0;
  flex-grow: 1;
}

/* Tag Row */
.card-tags {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 20px;
}

/* Card Footer */
.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 16px;
  border-top: 1px solid var(--border-color);
  gap: 12px;
}

/* Glass Header */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-color);
  transition: background-color var(--transition-normal), border-color var(--transition-normal);
}

.nav-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

/* Logo */
.brand-logo {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: inherit;
}

.brand-icon {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  background: var(--gradient-brand);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #ffffff;
  box-shadow: 0 3px 12px rgba(99, 102, 241, 0.3);
}

.brand-text h1 {
  font-size: 15px;
  font-weight: 800;
  margin: 0;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.brand-text p {
  font-size: 11px;
  color: var(--text-secondary);
  margin: 0;
  font-weight: 500;
}

/* Code & Monospace Utility */
.font-mono {
  font-family: var(--font-mono);
}

/* Glow Utility */
.celebration-glow {
  animation: pulseGlow 1.8s infinite ease-in-out;
  border-color: var(--color-success) !important;
}

@keyframes pulseGlow {
  0%, 100% {
    box-shadow: 0 0 15px rgba(16, 185, 129, 0.4), inset 0 0 15px rgba(16, 185, 129, 0.2);
  }
  50% {
    box-shadow: 0 0 30px rgba(16, 185, 129, 0.8), inset 0 0 25px rgba(16, 185, 129, 0.4);
  }
}

/* Unified Module Top Navigation Header */
.site-header, .module-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  height: 60px;
}

.header-container, .module-header-inner {
  max-width: 1360px;
  margin: 0 auto;
  padding: 0 20px;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.back-link, .nav-back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  font-size: 12px;
  font-weight: 600;
  text-decoration: none;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.back-link:hover, .nav-back-link:hover {
  background: var(--border-color);
  color: var(--text-primary);
  transform: translateY(-1px);
}

@media (max-width: 640px) {
  .site-header, .module-header {
    height: auto;
    min-height: 56px;
  }
  .header-container, .module-header-inner {
    padding: 8px 12px;
    gap: 8px;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
}