:root {
  font-family: system-ui, sans-serif;
  color: #e6e6e6;
  background: #0f1117;
}
body {
  margin: 0;
  padding: 1rem 1.25rem 3rem;
  max-width: 52rem;
  margin-inline: auto;
}
header {
  border-bottom: 1px solid #333;
  margin-bottom: 1.5rem;
  padding-bottom: 1rem;
}
header h1 {
  font-size: 1.35rem;
  margin: 0 0 0.35rem;
}
.stream {
  color: #9aa;
  font-size: 0.9rem;
  margin: 0;
}
a {
  color: #58a6ff;
}
.track {
  margin: 1.5rem 0;
}
.track h2 {
  font-size: 1.1rem;
  color: #8cf;
}
.pct {
  font-size: 0.85rem;
  color: #9aa;
}
.submodule-header {
  font-size: 0.95rem;
  color: #acf;
  margin: 1rem 0 0.5rem;
  border-top: 1px solid #333;
  padding-top: 0.75rem;
}
.lesson-card {
  display: block;
  padding: 0.75rem 1rem;
  margin: 0.5rem 0;
  background: #1c2128;
  border: 1px solid #333;
  border-radius: 8px;
  color: inherit;
  text-decoration: none;
}
.lesson-card:hover {
  border-color: #58a;
}
.lesson-card.done {
  border-color: #3fb950;
}
.lesson-card.locked {
  opacity: 0.75;
  border-style: dashed;
}
.timer {
  font-size: 2rem;
  font-variant-numeric: tabular-nums;
}
.quiz label {
  display: block;
  margin: 0.5rem 0;
}
.tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 1rem 0;
}
.tabs button {
  background: #1c2128;
  border: 1px solid #444;
  color: inherit;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  cursor: pointer;
}
.tabs button[aria-selected="true"] {
  border-color: #58a6ff;
}
.tab-panel.hidden {
  display: none;
}
.demo-md,
.doc-body {
  line-height: 1.55;
}
.demo-md code,
.doc-body code {
  background: #21262d;
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
}
.prereq-warn {
  background: #3d2a00;
  border: 1px solid #9a6700;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  margin: 1rem 0;
}
.error {
  color: #f85149;
}
.doc-excerpt {
  margin: 1rem 0;
  padding: 1rem;
  background: #1c2128;
  border-radius: 8px;
}
.doc-meta,
.doc-footer {
  font-size: 0.85rem;
  color: #9aa;
}
.assist-dialog {
  background: #1c2128;
  color: inherit;
  border: 1px solid #444;
  border-radius: 8px;
  padding: 1rem;
  max-width: 40rem;
}
.assist-dialog pre {
  white-space: pre-wrap;
  max-height: 50vh;
  overflow: auto;
}
.btn-row {
  margin: 1rem 0;
}
.btn-row button {
  background: #238636;
  border: none;
  color: #fff;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  cursor: pointer;
}
.video-fallback {
  background: #2d333b;
  border: 1px solid #444;
  border-radius: 8px;
  padding: 0.75rem 1rem;
  margin: 0.75rem 0;
  font-size: 0.95rem;
  color: #c9d1d9;
}
.lesson-video {
  margin: 0.75rem 0;
}
.lesson-video video {
  width: 100%;
  max-width: 720px;
  border-radius: 8px;
  background: #000;
}