/* Base */
:root {
  --bg: #1b1f24;
  --panel: #161b22;
  --muted: #9da7b3;
  --border: #30363d;
  --brand: #6ea8fe;
  --brand-2: #33adff;
  --success: #3fd074;
  --warning: #eab308;
  --danger: #ef4444;
}

*, *::before, *::after { box-sizing: border-box; }
html, body { overscroll-behavior: none; height: 100%; }
html { background-color: var(--bg); }
body {
  background-color: var(--bg);
  color: #e6edf3;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, Helvetica Neue, Arial, sans-serif;
  margin: 0;
  min-height: 100vh;
  font-size: 14px;
  display: flex;
  flex-direction: column;
}

/* Navbar */
.navbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 24px;
  background: rgba(13, 17, 23, 0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: #e6edf3;
}

.nav-brand img {
  height: 28px;
  width: auto;
  display: block;
}

.nav-title {
  font-size: 16px;
  font-weight: 600;
}

.nav-right {
  display: flex;
  align-items: center;
  gap: 12px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 18px;
  border-radius: 8px;
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  border: none;
  cursor: pointer;
  transition: transform 0.12s ease, filter 0.15s ease, background 0.15s ease, border-color 0.15s ease;
}

.btn:hover {
  transform: translateY(-1px);
}

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

.btn--primary {
  background: #238636;
  color: white;
}

.btn--primary:hover {
  filter: brightness(1.1);
}

.btn--secondary {
  background: rgba(255, 255, 255, 0.06);
  color: #e6edf3;
  border: 1px solid var(--border);
}

.btn--secondary:hover {
  background: rgba(255, 255, 255, 0.1);
  border-color: #4a5568;
}

.btn--sm {
  padding: 8px 14px;
  font-size: 12px;
}

/* Container */
.container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 24px;
  flex: 1;
  width: 100%;
}

/* Hero */
.hero {
  text-align: center;
  margin-bottom: 40px;
  padding: 32px 0;
}

.hero h1 {
  font-size: 32px;
  font-weight: 700;
  margin: 0 0 12px 0;
  letter-spacing: -0.02em;
}

.hero-subtitle {
  color: var(--muted);
  font-size: 16px;
  margin: 0;
  max-width: 500px;
  margin-left: auto;
  margin-right: auto;
}

/* Catalog Sections */
.catalog-section {
  margin-bottom: 48px;
}

.catalog-section:last-child {
  margin-bottom: 0;
}

.section-heading {
  font-size: 20px;
  font-weight: 600;
  margin: 0 0 20px 0;
  color: #e6edf3;
  letter-spacing: -0.01em;
}

/* Catalog Grid */
.catalog-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 24px;
}

/* Activity Card */
.activity-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  transition: border-color 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
}

.activity-card:hover {
  border-color: rgba(110, 168, 254, 0.4);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
}

.activity-thumbnail {
  width: 100%;
  aspect-ratio: 1 / 1;
  overflow: hidden;
  background: rgba(0, 0, 0, 0.2);
  display: block;
  text-decoration: none;
}

.activity-thumbnail--link {
  cursor: pointer;
  transition: opacity 0.15s ease;
}

.activity-thumbnail--link:hover {
  opacity: 0.85;
}

.activity-title-link {
  text-decoration: none;
  color: inherit;
}

.activity-title-link:hover .activity-title {
  color: var(--brand);
}

.activity-thumbnail img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.thumbnail-placeholder {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, rgba(30, 38, 50, 0.95) 0%, rgba(22, 27, 34, 0.95) 100%);
}

.placeholder-icon {
  font-size: 48px;
  opacity: 0.4;
}

.activity-content {
  padding: 16px;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.activity-type {
  display: inline-block;
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 4px 10px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.12);
  color: var(--muted);
  width: fit-content;
  font-weight: 500;
}

.type--flashcard {
  background: rgba(59, 130, 246, 0.15);
  border-color: rgba(59, 130, 246, 0.3);
  color: #93c5fd;
}

.type--quiz {
  background: rgba(139, 92, 246, 0.15);
  border-color: rgba(139, 92, 246, 0.3);
  color: #c4b5fd;
}

.type--keywords {
  background: rgba(234, 179, 8, 0.15);
  border-color: rgba(234, 179, 8, 0.3);
  color: #fde047;
}

.type--lesson {
  background: rgba(63, 208, 116, 0.15);
  border-color: rgba(63, 208, 116, 0.3);
  color: #86efac;
}

.activity-title {
  font-size: 16px;
  font-weight: 600;
  margin: 0;
  line-height: 1.4;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.activity-creator {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: auto;
  padding-top: 8px;
}

.creator-avatar {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  object-fit: cover;
}

.creator-avatar-placeholder {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: linear-gradient(135deg, #3b4450 0%, #2d333b 100%);
}

.creator-name {
  font-size: 13px;
  color: var(--muted);
}

.activity-actions {
  padding: 12px 16px;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  display: flex;
  gap: 8px;
}

.activity-actions .btn {
  flex: 1;
}

.copy-icon {
  font-size: 12px;
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 80px 24px;
  max-width: 400px;
  margin: 0 auto;
}

.empty-icon {
  font-size: 64px;
  opacity: 0.4;
  margin-bottom: 24px;
}

.empty-state h2 {
  font-size: 20px;
  margin: 0 0 12px 0;
}

.empty-state p {
  color: var(--muted);
  margin: 0 0 24px 0;
}

/* Footer */
.footer {
  padding: 24px;
  text-align: center;
  color: var(--muted);
  font-size: 12px;
  border-top: 1px solid var(--border);
}

.footer p {
  margin: 0;
}

/* Toast */
.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: var(--panel);
  border: 1px solid var(--border);
  padding: 12px 24px;
  border-radius: 8px;
  font-size: 13px;
  font-weight: 500;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
  opacity: 0;
  transition: transform 0.3s ease, opacity 0.3s ease;
  z-index: 100;
}

.toast--visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* Responsive */
@media (max-width: 768px) {
  .navbar {
    padding: 10px 16px;
  }

  .nav-title {
    display: none;
  }

  .container {
    padding: 16px;
  }

  .hero {
    margin-bottom: 24px;
    padding: 24px 0;
  }

  .hero h1 {
    font-size: 24px;
  }

  .hero-subtitle {
    font-size: 14px;
  }

  .catalog-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  .activity-actions {
    flex-direction: column;
  }

  /* Lesson detail responsive */
  .lesson-header {
    grid-template-columns: 1fr;
    gap: 24px;
  }

  .lesson-title {
    font-size: 22px;
  }

  .lesson-image-placeholder .placeholder-icon {
    font-size: 56px;
  }

  .lesson-actions {
    flex-direction: column;
  }
}

@media (max-width: 480px) {
  .navbar {
    padding: 8px 12px;
  }

  .nav-brand img {
    height: 24px;
  }

  .btn {
    padding: 8px 14px;
    font-size: 12px;
  }

  .container {
    padding: 12px;
  }

  .hero h1 {
    font-size: 20px;
  }

  .hero-subtitle {
    font-size: 13px;
  }

  .empty-state {
    padding: 48px 16px;
  }

  .empty-icon {
    font-size: 48px;
  }
}

/* Lesson Detail Page */
.lesson-detail {
  max-width: 1200px;
  margin: 0 auto;
}

.lesson-header {
  display: grid;
  grid-template-columns: 3fr 2fr;
  gap: 40px;
  align-items: start;
}

.lesson-image-wrap {
  aspect-ratio: 16 / 9;
  border-radius: 12px;
  overflow: hidden;
  background: rgba(0, 0, 0, 0.2);
  border: 1px solid var(--border);
}

.lesson-image {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.lesson-image-placeholder {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, rgba(30, 38, 50, 0.95) 0%, rgba(22, 27, 34, 0.95) 100%);
}

.lesson-image-placeholder .placeholder-icon {
  font-size: 72px;
  opacity: 0.4;
}

.lesson-info {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.lesson-badge {
  display: inline-block;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 6px 14px;
  border-radius: 999px;
  background: rgba(63, 208, 116, 0.15);
  border: 1px solid rgba(63, 208, 116, 0.3);
  color: #86efac;
  width: fit-content;
  font-weight: 500;
}

.lesson-title {
  font-size: 28px;
  font-weight: 700;
  margin: 0;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

.lesson-description {
  color: var(--muted);
  font-size: 15px;
  line-height: 1.6;
  margin: 0;
}

.lesson-creator {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px 0;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
}

.creator-avatar--lg {
  width: 48px;
  height: 48px;
}

.creator-info {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.creator-label {
  font-size: 11px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.lesson-meta {
  display: flex;
  gap: 12px;
}

.meta-item {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 12px 16px;
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid var(--border);
  border-radius: 10px;
  min-width: 100px;
}

.meta-label {
  font-size: 11px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.meta-value {
  font-size: 14px;
  font-weight: 500;
  color: #e6edf3;
}

.lesson-actions {
  display: flex;
  gap: 12px;
  margin-top: 8px;
}

.btn--lg {
  padding: 14px 24px;
  font-size: 15px;
}

/* Wide screens */
@media (min-width: 1600px) {
  .container {
    max-width: 1600px;
    padding: 32px 48px;
  }

  .catalog-grid {
    grid-template-columns: repeat(auto-fill, minmax(380px, 1fr));
    gap: 28px;
  }
}