/* ============================================================
   Math Repository — Styles
   ============================================================ */

:root {
  --bg-base: #06080f;
  --bg-surface: #0d1117;
  --bg-elevated: #161b22;
  --bg-card: rgba(22, 27, 34, 0.6);
  --bg-card-hover: rgba(22, 27, 34, 0.85);
  --border: rgba(255, 255, 255, 0.06);
  --border-hover: rgba(255, 255, 255, 0.14);
  --text: #e6edf3;
  --text-secondary: #8b949e;
  --text-muted: #484f58;
  --accent-green: #34d399;
  --accent-blue: #60a5fa;
  --accent-purple: #a78bfa;
  --accent-amber: #fbbf24;
  --accent-rose: #fb7185;
  --glass: rgba(255, 255, 255, 0.025);
  --glass-border: rgba(255, 255, 255, 0.07);
  --radius-lg: 20px;
  --radius: 14px;
  --radius-sm: 8px;
  --shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
  --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --max-width: 1200px;
}

/* Reset */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-base);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; text-decoration: none; }
button { font-family: inherit; cursor: pointer; border: none; background: none; color: inherit; }

/* Scrollbar */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.1); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: rgba(255,255,255,0.18); }

/* ---- Header ---- */
#header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(6, 8, 15, 0.75);
  backdrop-filter: blur(24px) saturate(180%);
  -webkit-backdrop-filter: blur(24px) saturate(180%);
  border-bottom: 1px solid var(--border);
}
.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 1.15rem;
  letter-spacing: -0.02em;
  transition: opacity var(--transition);
}
.logo:hover { opacity: 0.8; }
.logo-icon { font-size: 1.35rem; }

/* ---- Mode Toggle ---- */
.mode-toggle {
  position: relative;
  display: flex;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 3px;
}
.mode-btn {
  position: relative;
  z-index: 2;
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--text-secondary);
  border-radius: 8px;
  transition: color var(--transition);
  white-space: nowrap;
}
.mode-btn.active { color: var(--text); }
.mode-btn svg { flex-shrink: 0; }
.toggle-slider {
  position: absolute;
  top: 3px;
  left: 3px;
  height: calc(100% - 6px);
  width: calc(50% - 3px);
  background: rgba(255, 255, 255, 0.08);
  border-radius: 8px;
  transition: transform var(--transition);
}
.mode-toggle.advanced .toggle-slider {
  transform: translateX(100%);
}

/* ---- Breadcrumbs ---- */
.breadcrumbs {
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border);
}
.breadcrumb-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 10px 24px;
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.85rem;
  color: var(--text-secondary);
  overflow-x: auto;
  white-space: nowrap;
}
.breadcrumb-inner::-webkit-scrollbar { display: none; }
.crumb { transition: color var(--transition); }
.crumb:hover { color: var(--text); }
.crumb-sep { opacity: 0.3; user-select: none; }
.crumb-current { color: var(--text); font-weight: 600; }

/* ---- Main ---- */
.main-content {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px 24px 80px;
  min-height: calc(100vh - 64px);
}

/* Loading */
.loading-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 120px 0;
  color: var(--text-muted);
  gap: 16px;
}
.loading-spinner {
  width: 32px; height: 32px;
  border: 3px solid var(--border);
  border-top-color: var(--accent-blue);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ---- Home Hero ---- */
.home-hero {
  text-align: center;
  padding: 48px 0 40px;
}
.home-hero h1 {
  font-size: 2.8rem;
  font-weight: 800;
  letter-spacing: -0.04em;
  background: linear-gradient(135deg, var(--text) 0%, var(--text-secondary) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.home-hero p {
  font-size: 1.1rem;
  color: var(--text-secondary);
  margin-top: 8px;
}

/* ---- Course Cards (Home) ---- */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 20px;
  margin-top: 8px;
}
.course-card {
  position: relative;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 32px 28px;
  overflow: hidden;
  transition: transform var(--transition), border-color var(--transition), box-shadow var(--transition);
  backdrop-filter: blur(12px);
}
.course-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 4px;
  background: var(--accent);
}
.course-card::after {
  content: '';
  position: absolute;
  top: 0; right: 0;
  width: 180px; height: 180px;
  background: radial-gradient(circle, var(--accent), transparent 70%);
  opacity: 0.04;
  transform: translate(40%, -40%);
  transition: opacity var(--transition);
}
.course-card:hover {
  transform: translateY(-3px);
  border-color: var(--border-hover);
  box-shadow: 0 12px 40px rgba(0,0,0,0.3);
}
.course-card:hover::after { opacity: 0.08; }
.course-card.coming-soon {
  opacity: 0.45;
  cursor: default;
  pointer-events: none;
  --accent: var(--text-muted);
}
.course-card.coming-soon::before { background: var(--text-muted); }
.course-card.coming-soon::after { opacity: 0.02; }
.coming-soon-badge {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  padding: 2px 10px;
  border-radius: 8px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.course-card h2 {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}
.course-subtitle {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-top: 4px;
  font-weight: 400;
}
.course-meta {
  display: flex;
  gap: 8px;
  margin-top: 20px;
  font-size: 0.82rem;
  color: var(--text-muted);
}

/* ---- Resource Cards ---- */
.resource-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}
.resource-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px 22px;
  transition: transform var(--transition), border-color var(--transition), background var(--transition);
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
}
.resource-card::before {
  content: '';
  position: absolute;
  left: 0; top: 0;
  width: 3px; height: 100%;
  background: var(--accent);
  opacity: 0;
  transition: opacity var(--transition);
}
.resource-card:hover {
  transform: translateY(-2px);
  border-color: var(--border-hover);
  background: var(--bg-card-hover);
}
.resource-card:hover::before { opacity: 1; }
.resource-card h3 {
  font-size: 1.05rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}
.resource-card p {
  color: var(--text-secondary);
  font-size: 0.85rem;
  margin-top: 6px;
  flex: 1;
}
.resource-link {
  display: inline-block;
  margin-top: 16px;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--accent-rose);
  transition: opacity var(--transition);
}
.resource-card:hover .resource-link { opacity: 0.8; }

/* ---- Page Header ---- */
.page-header {
  margin-bottom: 28px;
}
.page-header h1 {
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}
.page-header p {
  color: var(--text-secondary);
  margin-top: 4px;
}

/* ---- Topic Cards ---- */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}
.topic-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 20px;
  transition: transform var(--transition), border-color var(--transition), background var(--transition);
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
}
.topic-card::before {
  content: '';
  position: absolute;
  left: 0; top: 0;
  width: 3px; height: 100%;
  background: var(--accent);
  opacity: 0;
  transition: opacity var(--transition);
}
.topic-card:hover {
  transform: translateY(-2px);
  border-color: var(--border-hover);
  background: var(--bg-card-hover);
}
.topic-card:hover::before { opacity: 1; }
.topic-card h3 {
  font-size: 1.05rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}
.topic-card .topic-desc {
  color: var(--text-secondary);
  font-size: 0.82rem;
  margin-top: 6px;
  flex: 1;
}
.topic-card .topic-meta {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-top: 14px;
  display: flex;
  align-items: center;
  gap: 6px;
}
.topic-alert-badge {
  display: inline-flex;
  align-items: center;
  gap: 3px;
  color: var(--accent-amber);
  font-size: 0.75rem;
  font-weight: 500;
}

/* ---- File Groups (Topic Detail) ---- */
.file-section {
  margin-bottom: 32px;
}
.file-section-header {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}
.file-section-header h3 {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}
.file-section-count {
  font-size: 0.72rem;
  color: var(--text-muted);
  background: var(--bg-elevated);
  padding: 2px 8px;
  border-radius: 10px;
}

/* ---- File Cards ---- */
.file-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 10px;
}
.file-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  background: var(--glass);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius-sm);
  transition: background var(--transition), border-color var(--transition), transform var(--transition);
}
.file-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-hover);
  transform: translateX(3px);
}
.file-icon {
  flex-shrink: 0;
  width: 36px; height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
}
.file-icon.pdf { background: rgba(239, 68, 68, 0.12); color: #ef4444; }
.file-icon.docx { background: rgba(59, 130, 246, 0.12); color: #3b82f6; }
.file-icon.other { background: rgba(156, 163, 175, 0.12); color: #9ca3af; }
.file-info { flex: 1; min-width: 0; }
.file-name {
  font-size: 0.88rem;
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.file-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 2px;
}
.file-size {
  font-size: 0.75rem;
  color: var(--text-muted);
}
.file-badge {
  font-size: 0.68rem;
  font-weight: 600;
  padding: 1px 7px;
  border-radius: 6px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.file-badge.lesson { background: rgba(52, 211, 153, 0.12); color: #34d399; }
.file-badge.practice { background: rgba(96, 165, 250, 0.12); color: #60a5fa; }
.file-badge.solutions { background: rgba(167, 139, 250, 0.12); color: #a78bfa; }
.file-badge.exam { background: rgba(251, 191, 36, 0.12); color: #fbbf24; }
.file-badge.reference { background: rgba(156, 163, 175, 0.12); color: #9ca3af; }
.file-open-icon {
  flex-shrink: 0;
  color: var(--text-muted);
  opacity: 0;
  transition: opacity var(--transition);
}
.file-card:hover .file-open-icon { opacity: 1; }

/* ---- Advanced Mode (File Explorer) ---- */
.explorer-list {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.explorer-row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  transition: background var(--transition);
}
.explorer-row:hover { background: var(--bg-elevated); }
.explorer-icon {
  flex-shrink: 0;
  font-size: 1.25rem;
  width: 28px;
  text-align: center;
}
.explorer-name {
  flex: 1;
  font-size: 0.9rem;
  min-width: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.explorer-name.dir { font-weight: 500; }
.explorer-size {
  flex-shrink: 0;
  font-size: 0.78rem;
  color: var(--text-muted);
  font-variant-numeric: tabular-nums;
}
.explorer-row.dir-row { cursor: pointer; }
.explorer-row.dir-row:hover .explorer-name { color: var(--accent-blue); }

/* Readme rendering */
.readme-block {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 28px;
  font-size: 0.9rem;
  line-height: 1.7;
  color: var(--text-secondary);
}
.readme-block h1, .readme-block h2, .readme-block h3 { color: var(--text); margin: 16px 0 8px; }
.readme-block p { margin: 8px 0; }
.readme-block code { background: rgba(255,255,255,0.06); padding: 2px 6px; border-radius: 4px; font-size: 0.85em; }
.readme-block a { color: var(--accent-blue); text-decoration: underline; }

/* ---- Alert Modal ---- */
.modal-overlay {
  position: fixed;
  inset: 0;
  z-index: 1000;
  background: rgba(0, 0, 0, 0.65);
  backdrop-filter: blur(8px);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s, visibility 0.3s;
}
.modal-overlay.visible {
  opacity: 1;
  visibility: visible;
}
.modal {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  max-width: 480px;
  width: 100%;
  overflow: hidden;
  transform: scale(0.95) translateY(10px);
  transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
  box-shadow: var(--shadow);
}
.modal-overlay.visible .modal {
  transform: scale(1) translateY(0);
}
.modal-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 20px 24px;
  border-bottom: 1px solid var(--border);
}
.modal-icon { font-size: 1.4rem; }
.modal-header h3 {
  flex: 1;
  font-size: 1.05rem;
  font-weight: 600;
}
.modal-close {
  width: 32px; height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  font-size: 1.3rem;
  color: var(--text-muted);
  transition: background var(--transition), color var(--transition);
}
.modal-close:hover { background: rgba(255,255,255,0.06); color: var(--text); }
.modal-body {
  padding: 20px 24px;
  font-size: 0.92rem;
  line-height: 1.6;
  color: var(--text-secondary);
}
.modal-footer {
  padding: 16px 24px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: flex-end;
}
.modal-btn {
  padding: 8px 20px;
  background: var(--accent-amber);
  color: #000;
  font-weight: 600;
  font-size: 0.85rem;
  border-radius: var(--radius-sm);
  transition: opacity var(--transition);
}
.modal-btn:hover { opacity: 0.85; }
.modal-btn-secondary {
  background: transparent;
  color: var(--text-secondary);
  border: 1px solid var(--border);
}
.modal-btn-secondary:hover { background: rgba(255,255,255,0.05); opacity: 1; }

/* ---- Animations ---- */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
.animate-in {
  animation: fadeInUp 0.35s ease-out both;
}
.delay-1 { animation-delay: 0.05s; }
.delay-2 { animation-delay: 0.1s; }
.delay-3 { animation-delay: 0.15s; }

/* ---- Empty State ---- */
.empty-state {
  text-align: center;
  padding: 80px 0;
  color: var(--text-muted);
}
.empty-state .empty-icon { font-size: 3rem; margin-bottom: 16px; }
.empty-state p { font-size: 1rem; }

/* ---- Responsive ---- */
@media (max-width: 768px) {
  .header-inner { padding: 0 16px; }
  .main-content { padding: 20px 16px 60px; }
  .home-hero h1 { font-size: 2rem; }
  .course-grid { grid-template-columns: 1fr; }
  .topic-grid { grid-template-columns: 1fr; }
  .resource-grid { grid-template-columns: 1fr; }
  .file-list { grid-template-columns: 1fr; }
  .mode-btn span:not(.icon) { display: none; }
  .breadcrumb-inner { padding: 8px 16px; }
}

@media (max-width: 480px) {
  .home-hero h1 { font-size: 1.65rem; }
  .home-hero p { font-size: 0.95rem; }
  .course-card { padding: 24px 20px; }
  .file-card { padding: 10px 12px; }
}