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

:root {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #21262d;
  --bg-hover: #30363d;
  --border: #30363d;
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --text-muted: #6e7681;
  --accent: #58a6ff;
  --accent-dim: #1f6feb;
  --green: #3fb950;
  --green-dim: #238636;
  --orange: #d29922;
  --red: #f85149;
  --purple: #bc8cff;
  --sidebar-width: 300px;
  --header-height: 48px;
  --font-mono: 'Cascadia Code', 'Fira Code', 'JetBrains Mono', 'Consolas', monospace;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
}

html { font-size: 15px; }
body {
  font-family: var(--font-sans);
  background: var(--bg-primary);
  color: var(--text-primary);
  display: flex;
  min-height: 100vh;
  overflow-x: hidden;
}

/* === Scrollbar === */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg-primary); }
::-webkit-scrollbar-thumb { background: var(--bg-tertiary); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--bg-hover); }

/* === Mobile Header === */
.mobile-header {
  display: none;
  position: fixed; top: 0; left: 0; right: 0;
  height: var(--header-height);
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  align-items: center;
  padding: 0 12px;
  gap: 12px;
  z-index: 1000;
}
.sidebar-toggle {
  background: none; border: none; cursor: pointer;
  display: flex; flex-direction: column; gap: 4px; padding: 4px;
}
.sidebar-toggle span {
  display: block; width: 20px; height: 2px;
  background: var(--text-primary); border-radius: 1px;
  transition: transform 0.2s;
}
.mobile-title { color: var(--green); font-family: var(--font-mono); font-size: 0.85rem; font-weight: 600; }
.mode-pills-mobile { margin-left: auto; display: flex; gap: 4px; }
.mode-pills-mobile .mode-pill { font-size: 0.7rem; padding: 4px 8px; }

/* === Sidebar === */
.sidebar {
  width: var(--sidebar-width);
  min-width: var(--sidebar-width);
  height: 100vh;
  position: sticky; top: 0;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  z-index: 100;
}
.sidebar-header { padding: 16px; border-bottom: 1px solid var(--border); }
.logo {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 12px;
}
.prompt { color: var(--green); }

.mode-pills { display: flex; gap: 4px; }
.mode-pill {
  flex: 1;
  padding: 6px 10px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-secondary);
  font-size: 0.8rem;
  font-family: var(--font-mono);
  cursor: pointer;
  transition: all 0.15s;
}
.mode-pill:hover { background: var(--bg-hover); color: var(--text-primary); }
.mode-pill.active {
  background: var(--accent-dim);
  border-color: var(--accent);
  color: #fff;
}

/* === Search === */
.search-container {
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  position: relative;
}
#searchInput {
  width: 100%;
  padding: 8px 12px;
  background: var(--bg-primary);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 0.85rem;
  outline: none;
  transition: border-color 0.15s;
}
#searchInput:focus { border-color: var(--accent); }
#searchInput::placeholder { color: var(--text-muted); }

.search-results {
  display: none;
  position: absolute;
  top: 100%; left: 16px; right: 16px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 6px;
  max-height: 300px;
  overflow-y: auto;
  z-index: 200;
  box-shadow: 0 8px 24px rgba(0,0,0,0.4);
}
.search-results.active { display: block; }
.search-result-item {
  padding: 8px 12px;
  cursor: pointer;
  border-bottom: 1px solid var(--border);
  font-size: 0.85rem;
}
.search-result-item:last-child { border-bottom: none; }
.search-result-item:hover { background: var(--bg-hover); }
.search-result-item .result-title { color: var(--accent); font-weight: 600; }
.search-result-item .result-context {
  color: var(--text-muted);
  font-size: 0.75rem;
  margin-top: 2px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.search-result-item mark {
  background: var(--orange);
  color: var(--bg-primary);
  border-radius: 2px;
  padding: 0 2px;
}

/* === Topic Tree === */
.topic-tree {
  flex: 1;
  overflow-y: auto;
  padding: 8px 0;
}
.tree-section { margin-bottom: 4px; }
.tree-section-header {
  display: flex;
  align-items: center;
  padding: 8px 16px;
  cursor: pointer;
  color: var(--text-secondary);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  user-select: none;
}
.tree-section-header:hover { color: var(--text-primary); }
.tree-section-header .chevron {
  margin-right: 6px;
  transition: transform 0.15s;
  font-size: 0.65rem;
}
.tree-section-header.expanded .chevron { transform: rotate(90deg); }
.tree-items { display: none; }
.tree-items.expanded { display: block; }
.tree-item {
  display: flex;
  align-items: center;
  padding: 6px 16px 6px 32px;
  cursor: pointer;
  color: var(--text-secondary);
  font-size: 0.85rem;
  transition: all 0.1s;
  gap: 8px;
  position: relative;
}
.tree-item:hover { background: var(--bg-hover); color: var(--text-primary); }
.tree-item.active {
  background: var(--bg-tertiary);
  color: var(--accent);
  border-left: 2px solid var(--accent);
}
.tree-item .read-indicator {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--green);
  margin-left: auto;
  flex-shrink: 0;
  display: none;
}
.tree-item.read .read-indicator { display: block; }

/* === Sidebar Footer === */
.sidebar-footer {
  padding: 12px 16px;
  border-top: 1px solid var(--border);
}
.progress-bar {
  height: 4px;
  background: var(--bg-tertiary);
  border-radius: 2px;
  overflow: hidden;
  margin-bottom: 6px;
}
.progress-fill {
  height: 100%;
  background: var(--green);
  border-radius: 2px;
  transition: width 0.3s;
}
.progress-text {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-family: var(--font-mono);
}

/* === Overlay === */
.sidebar-overlay {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0,0,0,0.5);
  z-index: 99;
}

/* === Main Content === */
.main-content {
  flex: 1;
  min-width: 0;
  overflow-y: auto;
  height: 100vh;
}
.content-view { padding: 32px; max-width: 900px; margin: 0 auto; }
.content-view.hidden { display: none; }

/* === Welcome Screen === */
.welcome { text-align: center; padding: 80px 20px; }
.welcome h1 { font-family: var(--font-mono); font-size: 1.8rem; margin-bottom: 12px; }
.welcome p { color: var(--text-secondary); font-size: 1.1rem; margin-bottom: 32px; }
.quick-stats { display: flex; justify-content: center; gap: 40px; margin-bottom: 32px; }
.stat { display: flex; flex-direction: column; align-items: center; }
.stat-num { font-size: 2rem; font-weight: 700; color: var(--accent); font-family: var(--font-mono); }
.stat-label { font-size: 0.85rem; color: var(--text-muted); margin-top: 4px; }
.keyboard-hints { color: var(--text-muted); font-size: 0.85rem; }
kbd {
  display: inline-block;
  padding: 2px 6px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.8rem;
}

/* === Markdown Body === */
.markdown-body { line-height: 1.7; }
.markdown-body h1 {
  font-size: 1.8rem;
  font-family: var(--font-mono);
  border-bottom: 1px solid var(--border);
  padding-bottom: 12px;
  margin-bottom: 24px;
}
.markdown-body h2 {
  font-size: 1.4rem;
  color: var(--accent);
  margin-top: 32px;
  margin-bottom: 16px;
  font-family: var(--font-mono);
}
.markdown-body h3 {
  font-size: 1.15rem;
  color: var(--green);
  margin-top: 24px;
  margin-bottom: 12px;
}
.markdown-body h4 { font-size: 1rem; color: var(--purple); margin-top: 20px; margin-bottom: 8px; }
.markdown-body p { margin-bottom: 12px; }
.markdown-body ul, .markdown-body ol { margin-bottom: 12px; padding-left: 24px; }
.markdown-body li { margin-bottom: 4px; }
.markdown-body li > ul, .markdown-body li > ol { margin-top: 4px; margin-bottom: 4px; }
.markdown-body strong { color: var(--orange); }
.markdown-body em { color: var(--text-secondary); }
.markdown-body a { color: var(--accent); text-decoration: none; }
.markdown-body a:hover { text-decoration: underline; }
.markdown-body hr { border: none; border-top: 1px solid var(--border); margin: 24px 0; }
.markdown-body blockquote {
  border-left: 3px solid var(--accent);
  padding: 8px 16px;
  margin: 12px 0;
  background: var(--bg-secondary);
  border-radius: 0 6px 6px 0;
  color: var(--text-secondary);
}
.markdown-body table {
  width: 100%;
  border-collapse: collapse;
  margin: 12px 0;
  font-size: 0.9rem;
}
.markdown-body th, .markdown-body td {
  padding: 8px 12px;
  border: 1px solid var(--border);
  text-align: left;
}
.markdown-body th {
  background: var(--bg-secondary);
  font-weight: 600;
  color: var(--accent);
}
.markdown-body tr:nth-child(even) { background: var(--bg-secondary); }

/* Code blocks */
.markdown-body code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--bg-tertiary);
  padding: 2px 6px;
  border-radius: 4px;
  color: var(--orange);
}
.markdown-body pre {
  position: relative;
  margin: 12px 0;
  border-radius: 8px;
  overflow: hidden;
}
.markdown-body pre code {
  display: block;
  padding: 16px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow-x: auto;
  color: var(--text-primary);
  font-size: 0.85rem;
  line-height: 1.5;
}
.copy-btn {
  position: absolute;
  top: 8px; right: 8px;
  padding: 4px 10px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text-muted);
  font-family: var(--font-mono);
  font-size: 0.7rem;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.15s;
  z-index: 5;
}
.markdown-body pre:hover .copy-btn { opacity: 1; }
.copy-btn:hover { color: var(--text-primary); background: var(--bg-hover); }
.copy-btn.copied { color: var(--green); border-color: var(--green-dim); }

/* Details/Summary (for quiz answers) */
.markdown-body details {
  margin: 12px 0;
  padding: 12px 16px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
}
.markdown-body details summary {
  cursor: pointer;
  color: var(--accent);
  font-weight: 600;
  font-family: var(--font-mono);
  font-size: 0.9rem;
}
.markdown-body details[open] summary { margin-bottom: 12px; }

/* === Cheatsheet Mode === */
.cheatsheet-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(400px, 1fr));
  gap: 16px;
  padding: 32px;
  max-width: 1400px;
  margin: 0 auto;
}
.cheatsheet-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}
.cheatsheet-card-header {
  padding: 12px 16px;
  background: var(--bg-tertiary);
  border-bottom: 1px solid var(--border);
  font-family: var(--font-mono);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--accent);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.cheatsheet-card-header .tag {
  font-size: 0.7rem;
  padding: 2px 8px;
  border-radius: 10px;
  background: var(--accent-dim);
  color: #fff;
  font-weight: 400;
}
.cheatsheet-card-body {
  padding: 12px 16px;
  font-size: 0.85rem;
  max-height: 400px;
  overflow-y: auto;
}
.cheatsheet-card-body pre code {
  font-size: 0.8rem;
  padding: 10px;
}

/* === Quiz Mode === */
.quiz-container { max-width: 800px; margin: 0 auto; }
.quiz-header { margin-bottom: 24px; }
.quiz-header h2 { font-family: var(--font-mono); margin-bottom: 16px; }
.quiz-controls { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }
#quizTopic {
  flex: 1; min-width: 200px;
  padding: 8px 12px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 0.85rem;
}
.btn {
  padding: 8px 20px;
  background: var(--accent-dim);
  border: 1px solid var(--accent);
  border-radius: 6px;
  color: #fff;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  cursor: pointer;
  transition: background 0.15s;
}
.btn:hover { background: var(--accent); }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

.quiz-placeholder { color: var(--text-muted); font-style: italic; padding: 40px 0; text-align: center; }

.quiz-progress { display: flex; align-items: center; gap: 12px; margin-bottom: 20px; }
.quiz-timer {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  color: var(--orange);
  min-width: 60px;
}
.quiz-timer.warning { color: var(--red); animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: 0.5; } }
.quiz-counter { color: var(--text-muted); font-family: var(--font-mono); font-size: 0.85rem; }
.quiz-progress .progress-bar { flex: 1; }

.quiz-question {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 24px;
  margin-bottom: 16px;
}
.quiz-question h3 { color: var(--text-primary); margin-bottom: 16px; font-size: 1rem; line-height: 1.5; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-option {
  padding: 12px 16px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.15s;
  font-family: var(--font-mono);
}
.quiz-option:hover { border-color: var(--accent); background: var(--bg-hover); }
.quiz-option.selected { border-color: var(--accent); background: var(--accent-dim); }
.quiz-option.correct { border-color: var(--green); background: var(--green-dim); color: #fff; }
.quiz-option.wrong { border-color: var(--red); background: #6e1010; }
.quiz-explanation {
  margin-top: 16px;
  padding: 12px 16px;
  background: var(--bg-primary);
  border-radius: 6px;
  border-left: 3px solid var(--green);
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.5;
}
.quiz-nav { display: flex; gap: 12px; justify-content: center; margin-top: 16px; }
.quiz-score {
  text-align: center;
  padding: 40px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
}
.quiz-score h2 { font-family: var(--font-mono); margin-bottom: 16px; }
.quiz-score .score-num { font-size: 3rem; font-weight: 700; font-family: var(--font-mono); }
.quiz-score .score-num.pass { color: var(--green); }
.quiz-score .score-num.fail { color: var(--red); }

/* === Responsive === */
@media (max-width: 768px) {
  .mobile-header { display: flex; }
  .sidebar {
    position: fixed;
    top: 0; left: 0; bottom: 0;
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    z-index: 200;
    padding-top: var(--header-height);
  }
  .sidebar.open { transform: translateX(0); }
  .sidebar-overlay.active { display: block; }
  .main-content { padding-top: var(--header-height); }
  .content-view { padding: 20px 16px; }
  .cheatsheet-grid { grid-template-columns: 1fr; padding: 20px 16px; }
  .quick-stats { gap: 20px; }
  .mode-pills { display: none; }
  .welcome { padding: 40px 10px; }
  .welcome h1 { font-size: 1.3rem; }
}

@media (min-width: 769px) {
  .mode-pills-mobile { display: none; }
}