:root {
  --bg: #0f1419;
  --panel: #1a2332;
  --card: #243044;
  --text: #e7eef8;
  --muted: #8fa3bb;
  --accent: #3d9cf0;
  --ok: #3ecf8e;
  --bad: #f07178;
  --warn: #e6c07b;
  --border: #334155;
  font-family: "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
.top {
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  align-items: flex-start;
}
.top h1 { margin: 0; font-size: 1.35rem; }
.sub { margin: 0.25rem 0 0; color: var(--muted); font-size: 0.9rem; }
.badge {
  font-size: 0.7rem;
  background: var(--accent);
  color: #041018;
  padding: 0.15rem 0.45rem;
  border-radius: 999px;
  vertical-align: middle;
}
.disclaimer {
  margin: 0;
  max-width: 24rem;
  font-size: 0.8rem;
  color: var(--warn);
  text-align: right;
}
.tabs {
  display: flex;
  gap: 0.25rem;
  padding: 0.75rem 1.5rem 0;
  flex-wrap: wrap;
}
.tab {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--muted);
  padding: 0.45rem 0.9rem;
  border-radius: 8px 8px 0 0;
  cursor: pointer;
}
.tab.active {
  background: var(--panel);
  color: var(--text);
  border-bottom-color: var(--panel);
}
main { flex: 1; padding: 0 1.5rem 1.5rem; background: var(--panel); margin: 0 1.5rem; border-radius: 0 12px 12px 12px; }
.panel { display: none; padding-top: 1rem; }
.panel.active { display: block; }
.row { display: flex; gap: 1rem; flex-wrap: wrap; margin-bottom: 1rem; }
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  flex: 1 1 280px;
}
.card.grow { flex: 2 1 400px; }
.card h2 { margin: 0 0 0.75rem; font-size: 1rem; }
label { display: block; margin: 0.5rem 0; font-size: 0.9rem; color: var(--muted); }
input, select {
  display: block;
  width: 100%;
  margin-top: 0.25rem;
  padding: 0.45rem 0.55rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: #0f172a;
  color: var(--text);
}
button {
  margin-top: 0.5rem;
  margin-right: 0.4rem;
  padding: 0.5rem 0.9rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: #334155;
  color: var(--text);
  cursor: pointer;
}
button.primary { background: var(--accent); border-color: var(--accent); color: #041018; font-weight: 600; }
button:disabled { opacity: 0.45; cursor: not-allowed; }
.muted { color: var(--muted); font-size: 0.85rem; }
.room-code { font-size: 1.4rem; font-weight: 700; letter-spacing: 0.12em; color: var(--ok); }
.concepts-box, .results, .follow-box {
  font-size: 0.9rem;
  line-height: 1.5;
}
.hw-hint {
  margin-top: 0.75rem;
  padding: 0.55rem 0.65rem;
  border: 1px dashed var(--border);
  border-radius: 8px;
  font-size: 0.85rem;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}
.step {
  border-left: 3px solid var(--border);
  padding: 0.4rem 0.6rem;
  margin: 0.4rem 0;
  background: #0f172a55;
}
.step.pass { border-color: var(--ok); }
.step.fail { border-color: var(--bad); }
.bin-pill {
  display: inline-block;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: #0f172a;
  border: 1px solid var(--border);
  margin-right: 0.35rem;
}
.bin-pill.good { border-color: var(--ok); color: var(--ok); }
.bin-pill.bad { border-color: var(--bad); color: var(--bad); }
#failMap {
  display: block;
  width: 100%;
  max-width: 320px;
  background: #0b1220;
  border-radius: 8px;
  border: 1px solid var(--border);
}
.repair-box {
  margin-top: 0.5rem;
  padding: 0.5rem;
  border-radius: 8px;
  background: #0f172a55;
  border: 1px solid var(--border);
  font-size: 0.85rem;
}
.log {
  margin: 0;
  max-height: 220px;
  overflow: auto;
  background: #0b1220;
  padding: 0.75rem;
  border-radius: 8px;
  font-size: 0.8rem;
  color: #cbd5e1;
}
.stage-controls, .stage-nav { margin: 0.75rem 0; }
.stage-btn.active { outline: 2px solid var(--accent); }
.stage-chip {
  display: inline-block;
  margin: 0.2rem 0.25rem 0 0;
  padding: 0.25rem 0.5rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  font-size: 0.75rem;
  background: #0f172a;
  cursor: pointer;
  color: var(--muted);
}
.stage-chip.on { border-color: var(--accent); color: var(--text); }
footer {
  padding: 0.75rem 1.5rem;
  color: var(--muted);
  font-size: 0.8rem;
  display: flex;
  gap: 0.5rem;
}
ul { padding-left: 1.2rem; }
code { font-family: ui-monospace, monospace; font-size: 0.85em; }

.chapter-list { display: flex; flex-direction: column; gap: 0.35rem; max-height: 70vh; overflow: auto; }
.chapter-btn {
  text-align: left;
  width: 100%;
  margin: 0;
}
.chapter-btn.current {
  outline: 2px solid var(--accent);
  background: #1e3a5f;
}
.chapter-btn .cid {
  display: block;
  font-size: 0.75rem;
  color: var(--muted);
  font-family: ui-monospace, monospace;
}
.tutorial-body {
  font-size: 0.92rem;
  line-height: 1.55;
  background: #0f172a55;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.9rem 1rem;
  max-height: 60vh;
  overflow: auto;
}
.tutorial-body > *:first-child { margin-top: 0; }
.tutorial-body > *:last-child { margin-bottom: 0; }
.tutorial-body h1,
.tutorial-body h2,
.tutorial-body h3,
.tutorial-body h4 {
  margin: 1rem 0 0.45rem;
  line-height: 1.3;
  color: var(--text);
}
.tutorial-body h1 { font-size: 1.25rem; }
.tutorial-body h2 { font-size: 1.1rem; }
.tutorial-body h3 { font-size: 1rem; }
.tutorial-body p,
.tutorial-body ul,
.tutorial-body ol,
.tutorial-body blockquote,
.tutorial-body pre,
.tutorial-body table {
  margin: 0.55rem 0;
}
.tutorial-body ul,
.tutorial-body ol {
  padding-left: 1.3rem;
}
.tutorial-body li { margin: 0.2rem 0; }
.tutorial-body blockquote {
  margin-left: 0;
  padding: 0.45rem 0.75rem;
  border-left: 3px solid var(--accent, #38bdf8);
  background: #0b1220;
  color: var(--muted);
}
.tutorial-body code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.85em;
  background: #020617;
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
}
.tutorial-body pre {
  background: #020617;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.7rem 0.85rem;
  overflow: auto;
}
.tutorial-body pre code {
  background: transparent;
  padding: 0;
}
.tutorial-body table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.88rem;
}
.tutorial-body th,
.tutorial-body td {
  border: 1px solid var(--border);
  padding: 0.35rem 0.5rem;
  text-align: left;
  vertical-align: top;
}
.tutorial-body th {
  background: #0b1220;
}
.tutorial-body hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 1rem 0;
}
.tutorial-body a { color: var(--accent, #38bdf8); }

.tutorial-meta { margin-bottom: 0.5rem; }
.sync-banner {
  padding: 0.45rem 0.6rem;
  border-radius: 6px;
  background: #0f172a;
  border: 1px dashed var(--border);
}
.sync-banner.live {
  border-color: var(--ok);
  color: var(--ok);
}

.quiz-box { display: flex; flex-direction: column; gap: 1rem; }
.quiz-item {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.75rem;
  background: #0f172a55;
}
.quiz-item h3 { margin: 0 0 0.5rem; font-size: 0.95rem; }
.quiz-options label {
  display: flex;
  align-items: flex-start;
  gap: 0.4rem;
  color: var(--text);
  cursor: pointer;
  margin: 0.35rem 0;
}
.quiz-options input { width: auto; margin: 0.15rem 0 0; }
.order-list { display: flex; flex-direction: column; gap: 0.35rem; }
.order-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.4rem 0.55rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: #0f172a;
  cursor: pointer;
}
.order-item .ord {
  min-width: 1.5rem;
  height: 1.5rem;
  border-radius: 999px;
  background: #334155;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
}
.order-item.picked { border-color: var(--accent); }
.quiz-result {
  margin-top: 0.75rem;
  padding: 0.75rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #0f172a;
  font-size: 0.9rem;
  line-height: 1.5;
  display: none;
}
.quiz-result.show { display: block; }
.quiz-result.ok { border-color: var(--ok); }
.quiz-result.bad { border-color: var(--bad); }
.explain { color: var(--muted); font-size: 0.85rem; margin-top: 0.25rem; }