/* ============================================
   LEARNING TOPICS LANDING PAGE — Design System
   ============================================
   Follows the frontend-design skill direction:
   - Display: JetBrains Mono (code-native, distinctive)
   - Body: Inter
   - Accent signature: emerald (#10b981) for learning/growth
   - Amber (#f59e0b) for active/search highlights
   - Violet (#a78bfa) for advanced topics
   - Deep navy background (#080c14 / #111827)
   ============================================ */

/* ─── CSS Variables (scoped to learning-topics page) ─── */
[data-page='learning-topics'] {
  --lt-bg: #080c14;
  --lt-surface: #111827;
  --lt-elevated: #1e293b;
  --lt-primary: #10b981;
  --lt-primary-rgb: 16, 185, 129;
  --lt-accent: #f59e0b;
  --lt-accent-rgb: 245, 158, 11;
  --lt-violet: #a78bfa;
  --lt-violet-rgb: 167, 139, 250;
  --lt-cyan: #06b6d4;
  --lt-text: #f1f5f9;
  --lt-text-muted: #64748b;
  --lt-border: rgba(16, 185, 129, 0.1);
  --lt-border-hover: rgba(16, 185, 129, 0.2);
  --lt-radius: 12px;
  --lt-radius-lg: 20px;
  --lt-pastel-red: #ffb3ba;
  --lt-pastel-red-rgb: 255, 179, 186;
}

/* ─── Hero Section ─── */
[data-page='learning-topics'] .lt-hero {
  position: relative;
  padding: 8rem 1.5rem 3rem;
  text-align: center;
  overflow: hidden;
  background: var(--lt-bg);
  min-height: 60vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.lt-hero-bg {
  position: absolute;
  inset: 0;
  z-index: 0;
  overflow: hidden;
}

.lt-hero-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(16, 185, 129, 0.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(16, 185, 129, 0.025) 1px, transparent 1px);
  background-size: 48px 48px;
  mask-image: radial-gradient(ellipse 60% 50% at 50% 40%, black 30%, transparent 70%);
  -webkit-mask-image: radial-gradient(ellipse 60% 50% at 50% 40%, black 30%, transparent 70%);
}

.lt-hero-glow {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.lt-hero-content {
  position: relative;
  z-index: 1;
  max-width: 720px;
  width: 100%;
}

.lt-hero-title {
  font-family: 'JetBrains Mono', monospace;
  font-size: clamp(2.5rem, 6vw, 4.5rem);
  font-weight: 700;
  color: #bef5cb;
  line-height: 1.1;
  margin-bottom: 1rem;
  letter-spacing: -1px;
  display: inline-flex;
  flex-wrap: wrap;
  justify-content: center;
  cursor: default;
}

/* ─── Heading Glitch Letters ─── */
.lt-title-letter {
  display: inline-block;
  position: relative;
}

.lt-title-letter .lt-letter-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.15s ease;
  background: #080c14; /* match page background to fully cover DOM text */
  image-rendering: pixelated;
  -ms-interpolation-mode: nearest-neighbor;
}

.lt-title-letter.lt-glitching .lt-letter-canvas {
  opacity: 1;
}

.lt-title-space {
  display: inline-block;
  width: 0.3em;
}

.lt-hero-subtitle {
  font-family: 'Inter', sans-serif;
  font-size: 1.05rem;
  color: var(--lt-text-muted);
  line-height: 1.6;
  max-width: 540px;
  margin: 0 auto 2rem;
}

/* ─── Search ─── */
.lt-search-wrapper {
  max-width: 480px;
  margin: 0 auto 1.5rem;
}

.lt-search {
  position: relative;
  display: flex;
  align-items: center;
  background: var(--lt-surface);
  border: 1px solid var(--lt-border);
  border-radius: 100px;
  transition: all 0.25s ease;
  overflow: hidden;
}

.lt-search:focus-within {
  border-color: #a5b4fc;
  box-shadow:
    0 0 0 3px rgba(165, 180, 252, 0.1),
    0 4px 20px rgba(165, 180, 252, 0.04);
  background: #141e33;
}

.lt-search-icon {
  position: absolute;
  left: 16px;
  color: var(--lt-text-muted);
  font-size: 0.9rem;
  pointer-events: none;
  transition: color 0.25s ease;
}

.lt-search:focus-within .lt-search-icon {
  color: #a5b4fc;
}

.lt-search-input {
  flex: 1;
  padding: 0.85rem 3rem 0.85rem 2.75rem;
  background: transparent;
  border: none;
  color: var(--lt-text);
  font-family: 'Inter', sans-serif;
  font-size: 0.95rem;
  outline: none;
}

.lt-search-input::placeholder {
  color: var(--lt-text-muted);
  opacity: 0.6;
}

.lt-clear-btn {
  position: absolute;
  right: 44px;
  background: none;
  border: none;
  color: var(--lt-text-muted);
  cursor: pointer;
  padding: 4px 6px;
  font-size: 0.85rem;
  border-radius: 50%;
  display: none;
  transition: all 0.2s ease;
}

.lt-clear-btn:hover {
  color: #ef4444;
  background: rgba(239, 68, 68, 0.1);
}

.lt-clear-btn.visible {
  display: flex;
}

.lt-search-hint {
  position: absolute;
  right: 14px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem;
  color: var(--lt-text-muted);
  opacity: 0.4;
  pointer-events: none;
  padding: 2px 6px;
  border: 1px solid var(--lt-border);
  border-radius: 4px;
}

/* ─── Filter Chips ─── */
.lt-filters {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
  padding: 0 0.5rem;
}

.lt-filter-chip {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  font-weight: 500;
  padding: 0.45rem 1rem;
  border-radius: 100px;
  background: transparent;
  border: 1px solid var(--lt-border);
  color: var(--lt-text-muted);
  cursor: pointer;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.lt-filter-chip:hover {
  border-color: var(--lt-primary);
  color: var(--lt-primary);
  background: rgba(var(--lt-primary-rgb), 0.06);
}

.lt-filter-chip.active {
  background: rgba(165, 180, 252, 0.12);
  border-color: #a5b4fc;
  color: #a5b4fc;
  box-shadow: 0 0 12px rgba(165, 180, 252, 0.08);
}

.lt-result-count {
  font-family: 'Inter', sans-serif;
  font-size: 0.85rem;
  color: var(--lt-text-muted);
  margin-top: 0.5rem;
}

.lt-result-count span {
  color: var(--lt-primary);
  font-weight: 600;
  font-family: 'JetBrains Mono', monospace;
}

/* ─── Section ─── */
.lt-section {
  padding: 2rem 1.5rem 5rem;
  background: var(--lt-bg);
}

.lt-container {
  max-width: 1200px;
  margin: 0 auto;
}

/* ─── Card Grid ─── */
.lt-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}

@media (min-width: 1024px) {
  .lt-grid {
    grid-template-columns: repeat(4, 1fr);
  }
}

@media (max-width: 768px) {
  .lt-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

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

/* ─── Card ─── */
.lt-card {
  position: relative;
  background: var(--lt-surface);
  border: 1px solid var(--lt-border);
  border-radius: var(--lt-radius);
  padding: 1.25rem;
  transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  cursor: pointer;
  text-decoration: none;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  isolation: isolate;
  overflow: hidden;
}

.lt-card::before {
  content: '';
  position: absolute;
  inset: -1px;
  border-radius: var(--lt-radius);
  background: linear-gradient(135deg, rgba(var(--lt-primary-rgb), 0.08), transparent 60%);
  opacity: 0;
  transition: opacity 0.3s ease;
  z-index: -1;
}

.lt-card:hover {
  border-color: var(--lt-border-hover);
  transform: translateY(-3px);
  box-shadow: 0 8px 30px rgba(0, 0, 0, 0.3);
}

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

.lt-card:focus-visible {
  outline: 2px solid var(--lt-primary);
  outline-offset: 2px;
}

.lt-card-icon {
  font-size: 1.5rem;
  line-height: 1;
  margin-bottom: 0.25rem;
  color: inherit;
}

.lt-card-title {
  font-family: 'Inter', sans-serif;
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--lt-text);
  line-height: 1.3;
}

.lt-card-desc {
  font-family: 'Inter', sans-serif;
  font-size: 0.78rem;
  color: var(--lt-text-muted);
  line-height: 1.5;
  flex: 1;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.lt-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  padding-top: 0.5rem;
  border-top: 1px solid var(--lt-border);
}

.lt-card-category {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.6rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  max-width: 70%;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* Category-specific badge colors */
.lt-card[data-category='data-structures'] .lt-card-category {
  color: #34d399;
  border-color: rgba(52, 211, 153, 0.15);
  background: rgba(52, 211, 153, 0.06);
  border: 1px solid rgba(52, 211, 153, 0.1);
}

.lt-card[data-category='core-algorithms'] .lt-card-category {
  color: #38bdf8;
  border-color: rgba(56, 189, 248, 0.15);
  background: rgba(56, 189, 248, 0.06);
  border: 1px solid rgba(56, 189, 248, 0.1);
}

.lt-card[data-category='advanced-algorithms'] .lt-card-category {
  color: var(--lt-violet);
  border-color: rgba(var(--lt-violet-rgb), 0.15);
  background: rgba(var(--lt-violet-rgb), 0.06);
  border: 1px solid rgba(var(--lt-violet-rgb), 0.1);
}

.lt-card[data-category='special'] .lt-card-category {
  color: var(--lt-accent);
  border-color: rgba(var(--lt-accent-rgb), 0.15);
  background: rgba(var(--lt-accent-rgb), 0.06);
  border: 1px solid rgba(var(--lt-accent-rgb), 0.1);
}

.lt-card-arrow {
  color: var(--lt-text-muted);
  font-size: 0.75rem;
  transition: all 0.2s ease;
  flex-shrink: 0;
}

.lt-card:hover .lt-card-arrow {
  color: var(--lt-primary);
  transform: translateX(3px);
}

/* ─── Empty State ─── */
.lt-empty {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--lt-text-muted);
}

.lt-empty i {
  font-size: 2.5rem;
  margin-bottom: 1rem;
  opacity: 0.4;
}

.lt-empty h3 {
  font-family: 'JetBrains Mono', monospace;
  font-size: 1.2rem;
  color: var(--lt-text);
  margin-bottom: 0.5rem;
}

.lt-empty p {
  font-family: 'Inter', sans-serif;
  font-size: 0.9rem;
}

/* ─── Responsive ─── */
@media (max-width: 768px) {
  [data-page='learning-topics'] .lt-hero {
    padding: 6rem 1rem 2.5rem;
    min-height: auto;
  }

  .lt-hero-title {
    font-size: 2rem;
  }

  .lt-hero-subtitle {
    font-size: 0.9rem;
  }

  .lt-search-input {
    font-size: 0.9rem;
    padding: 0.75rem 2.5rem 0.75rem 2.5rem;
  }

  .lt-filters {
    gap: 0.35rem;
  }

  .lt-filter-chip {
    font-size: 0.7rem;
    padding: 0.35rem 0.75rem;
  }

  .lt-grid {
    gap: 0.75rem;
  }

  .lt-search-hint {
    display: none;
  }
}

/* ─── Back Button ─── */
.lt-back-btn {
  position: absolute;
  top: 2rem;
  left: 1.5rem;
  z-index: 10;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.55rem 1rem 0.55rem 0.85rem;
  background: var(--lt-surface);
  border: 1px solid var(--lt-border);
  border-radius: 100px;
  color: var(--lt-text-muted);
  font-family: 'Inter', sans-serif;
  font-size: 0.85rem;
  cursor: pointer;
  transition: all 0.2s ease;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.lt-back-btn i {
  font-size: 0.85rem;
  transition: transform 0.2s ease;
}

.lt-back-btn span {
  font-weight: 500;
}

.lt-back-btn:hover {
  border-color: var(--lt-pastel-red);
  color: var(--lt-pastel-red);
  background: rgba(var(--lt-pastel-red-rgb), 0.08);
}

.lt-back-btn:hover i {
  transform: translateX(-3px);
}

.lt-back-btn:focus-visible {
  outline: 2px solid var(--lt-pastel-red);
  outline-offset: 2px;
}

@media (max-width: 768px) {
  .lt-back-btn {
    top: 1rem;
    left: 0.75rem;
    padding: 0.45rem 0.75rem 0.45rem 0.65rem;
    font-size: 0.8rem;
  }
  .lt-back-btn span {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .lt-back-btn {
    transition: none;
  }
  .lt-back-btn i {
    transition: none;
  }
  .lt-back-btn:hover i {
    transform: none;
  }

  .lt-card {
    animation: none;
  }

  .lt-card:hover {
    transform: none;
  }

  .lt-card:hover .lt-card-arrow {
    transform: none;
  }

  .lt-search {
    transition: none;
  }

  .lt-filter-chip {
    transition: none;
  }

  .lt-title-letter.lt-glitching .lt-letter-canvas {
    opacity: 1;
    transition: none;
  }
}