*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #0d1117;
  --surface: #161b22;
  --surface2: #21262d;
  --border: #30363d;
  --text: #e6edf3;
  --text-dim: #8b949e;
  --accent: #58a6ff;
  --accent2: #3fb950;
  --accent3: #d29922;
  --accent4: #f85149;
  --purple: #bc8cff;
  --cyan: #39d4ff;
}

html, body {
  height: 100%;
  width: 100%;
  overflow: hidden;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  font-size: 15px;
}

#ai101 {
  display: flex;
  flex-direction: column;
  height: 100vh;
  width: 100vw;
}

/* ---- Header ---- */
#ai-header {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  padding: 0.65rem 1.5rem;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
  z-index: 10;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 0.7rem;
  flex-shrink: 0;
}

.header-logo {
  font-size: 1.8rem;
  line-height: 1;
}

.header-name {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--accent);
  line-height: 1.1;
}

.header-sub {
  font-size: 0.72rem;
  color: var(--text-dim);
}

.header-progress {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  flex: 1;
}

.progress-track {
  flex: 1;
  height: 6px;
  background: var(--surface2);
  border-radius: 3px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--purple));
  border-radius: 3px;
  transition: width 0.5s ease;
  width: 0%;
}

.progress-label {
  font-size: 0.78rem;
  color: var(--text-dim);
  white-space: nowrap;
  flex-shrink: 0;
}

/* ---- Body layout ---- */
#ai-body {
  display: flex;
  flex: 1;
  min-height: 0;
}

/* ---- Sidebar ---- */
#ai-sidebar {
  width: 250px;
  flex-shrink: 0;
  background: var(--surface);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
}

.sidebar-home {
  padding: 0.75rem 1.2rem;
  font-size: 0.82rem;
  color: var(--text-dim);
  cursor: pointer;
  border-bottom: 1px solid var(--border);
  transition: color 0.15s;
}

.sidebar-home:hover {
  color: var(--accent);
}

#lesson-list {
  padding: 0.5rem 0;
}

.lesson-item {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.55rem 1rem;
  cursor: pointer;
  border-left: 3px solid transparent;
  transition: background 0.12s, border-color 0.12s;
}

.lesson-item:hover {
  background: var(--surface2);
}

.lesson-item.active {
  background: rgba(88, 166, 255, 0.1);
  border-left-color: var(--accent);
}

.lesson-dot {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  border: 2px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.68rem;
  font-weight: 600;
  color: var(--text-dim);
  flex-shrink: 0;
  transition: all 0.2s;
}

.lesson-item.active .lesson-dot {
  border-color: var(--accent);
  color: var(--accent);
}

.lesson-item.done .lesson-dot {
  background: var(--accent2);
  border-color: var(--accent2);
  color: var(--bg);
  font-size: 0.8rem;
}

.lesson-meta {
  flex: 1;
  min-width: 0;
}

.lesson-num {
  font-size: 0.65rem;
  color: var(--text-dim);
  line-height: 1;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.lesson-name {
  font-size: 0.82rem;
  color: var(--text);
  line-height: 1.3;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.lesson-item.active .lesson-name {
  color: var(--accent);
}

/* ---- Content ---- */
#ai-content {
  flex: 1;
  overflow-y: auto;
  padding: 2rem 2.5rem;
}

/* ---- Welcome ---- */
.welcome-wrap {
  text-align: center;
  max-width: 600px;
  margin: 2rem auto;
  padding: 1rem;
}

.welcome-icon {
  font-size: 4rem;
  margin-bottom: 1rem;
  display: block;
}

.welcome-wrap h2 {
  font-size: 2.4rem;
  font-weight: 800;
  margin-bottom: 0.75rem;
  background: linear-gradient(135deg, var(--accent), var(--purple));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.welcome-wrap > p {
  font-size: 1rem;
  color: var(--text-dim);
  line-height: 1.6;
  margin-bottom: 2rem;
}

.start-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 2rem;
  background: var(--accent);
  border: none;
  border-radius: 10px;
  color: var(--bg);
  font-size: 1rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s;
  margin-bottom: 2.5rem;
}

.start-btn:hover {
  background: #79b8ff;
  transform: translateY(-2px);
}

.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(170px, 1fr));
  gap: 0.7rem;
  text-align: left;
}

.course-item {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.8rem;
  cursor: pointer;
  transition: border-color 0.15s, transform 0.1s;
}

.course-item:hover {
  border-color: var(--accent);
  transform: translateY(-1px);
}

.ci-icon {
  font-size: 1.3rem;
  margin-bottom: 0.3rem;
}

.ci-num {
  font-size: 0.65rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.ci-title {
  font-size: 0.82rem;
  color: var(--text);
  font-weight: 500;
  line-height: 1.3;
}

/* ---- Lesson content ---- */
.lesson-header {
  margin-bottom: 1.5rem;
}

.lesson-part-label {
  font-size: 0.72rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.35rem;
}

.lesson-header h2 {
  font-size: 1.9rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.2;
  margin-bottom: 0.4rem;
}

.lesson-subtitle {
  font-size: 0.95rem;
  color: var(--text-dim);
}

/* ---- Diagram ---- */
.diagram-wrap {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.5rem 1rem;
  margin: 1.2rem 0 1.5rem;
  text-align: center;
}

.diagram-wrap svg {
  max-width: 100%;
  height: auto;
}

.diagram-caption {
  font-size: 0.78rem;
  color: var(--text-dim);
  margin-top: 0.6rem;
  font-style: italic;
}

/* ---- Body text ---- */
.lesson-body {
  line-height: 1.72;
  color: var(--text);
  max-width: 780px;
}

.lesson-body p {
  margin-bottom: 0.9rem;
}

.lesson-body h3 {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--accent);
  margin: 1.5rem 0 0.5rem;
}

.lesson-body h4 {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--accent3);
  margin: 1.1rem 0 0.35rem;
}

.lesson-body ul, .lesson-body ol {
  margin: 0.4rem 0 0.9rem 1.4rem;
}

.lesson-body li {
  margin-bottom: 0.25rem;
  font-size: 0.93rem;
}

.lesson-body strong {
  color: var(--cyan);
  font-weight: 600;
}

.lesson-body em {
  color: var(--text-dim);
  font-style: italic;
}

.lesson-body code {
  font-family: 'SF Mono', 'Fira Code', 'Consolas', monospace;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.1em 0.4em;
  font-size: 0.85em;
  color: var(--accent3);
}

/* ---- Callout boxes ---- */
.callout {
  border-radius: 8px;
  padding: 0.9rem 1.1rem;
  margin: 1rem 0;
  font-size: 0.92rem;
}

.callout-title {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 0.4rem;
}

.callout.blue {
  background: rgba(88, 166, 255, 0.08);
  border: 1px solid rgba(88, 166, 255, 0.25);
}

.callout.blue .callout-title { color: var(--accent); }

.callout.green {
  background: rgba(63, 185, 80, 0.08);
  border: 1px solid rgba(63, 185, 80, 0.25);
}

.callout.green .callout-title { color: var(--accent2); }

.callout.yellow {
  background: rgba(210, 153, 34, 0.08);
  border: 1px solid rgba(210, 153, 34, 0.25);
}

.callout.yellow .callout-title { color: var(--accent3); }

/* ---- Info cards ---- */
.info-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: 0.75rem;
  margin: 0.9rem 0;
}

.info-card {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.9rem;
}

.ic-icon {
  font-size: 1.4rem;
  margin-bottom: 0.3rem;
}

.ic-title {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.25rem;
}

.ic-desc {
  font-size: 0.78rem;
  color: var(--text-dim);
  line-height: 1.4;
}

/* ---- Video links ---- */
.videos-section {
  margin-top: 2rem;
  padding-top: 1.2rem;
  border-top: 1px solid var(--border);
  max-width: 780px;
}

.videos-section h3 {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-dim);
  margin-bottom: 0.7rem;
}

.video-links {
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.video-link {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.13s, transform 0.1s;
}

.video-link:hover {
  border-color: var(--accent);
  transform: translateX(2px);
}

.vl-play {
  width: 28px;
  height: 28px;
  background: #ff0000;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7rem;
  flex-shrink: 0;
}

.vl-info {
  flex: 1;
  min-width: 0;
}

.vl-title {
  font-size: 0.88rem;
  font-weight: 500;
  line-height: 1.3;
}

.vl-channel {
  font-size: 0.75rem;
  color: var(--text-dim);
}

.vl-arrow {
  color: var(--text-dim);
  font-size: 0.8rem;
  flex-shrink: 0;
}

/* ---- Navigation ---- */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 2.5rem;
  padding-top: 1.2rem;
  border-top: 1px solid var(--border);
  max-width: 780px;
  gap: 0.75rem;
}

.nav-btn {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.55rem 1.1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  cursor: pointer;
  font-size: 0.85rem;
  transition: all 0.13s;
  white-space: nowrap;
}

.nav-btn:hover:not(:disabled) {
  border-color: var(--accent);
  color: var(--accent);
}

.nav-btn:disabled {
  opacity: 0.35;
  cursor: default;
}

.nav-btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--bg);
  font-weight: 700;
}

.nav-btn.primary:hover:not(:disabled) {
  background: #79b8ff;
  border-color: #79b8ff;
  color: var(--bg);
}

.mark-btn {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.5rem 1rem;
  background: transparent;
  border: 1px solid var(--accent2);
  border-radius: 8px;
  color: var(--accent2);
  cursor: pointer;
  font-size: 0.82rem;
  transition: all 0.13s;
  white-space: nowrap;
}

.mark-btn:hover, .mark-btn.done {
  background: var(--accent2);
  color: var(--bg);
  font-weight: 600;
}

/* ---- Scrollbars ---- */
#ai-sidebar::-webkit-scrollbar,
#ai-content::-webkit-scrollbar {
  width: 5px;
}

#ai-sidebar::-webkit-scrollbar-track,
#ai-content::-webkit-scrollbar-track {
  background: transparent;
}

#ai-sidebar::-webkit-scrollbar-thumb,
#ai-content::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 3px;
}

/* ---- Responsive ---- */
@media (max-width: 720px) {
  #ai-sidebar { width: 195px; }
  #ai-content { padding: 1.2rem; }
}

@media (max-width: 520px) {
  #ai-sidebar { width: 44px; }
  .lesson-meta, .sidebar-home span + * { display: none; }
  .lesson-dot { margin: 0 auto; }
}