:root {
  --bg: #f4f1ea;
  --ink: #1c1915;
  --muted: #5c564c;
  --line: #e2d9cc;
  --card: #fffcf7;
  --green: #1b5e45;
  --green-soft: #e5f2eb;
  --amber: #8a5a12;
  --amber-soft: #fbf3e4;
  --red: #8d2f2f;
  --max: 44rem;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 18px/1.55 "Segoe UI", "PingFang HK", "Microsoft JhengHei", sans-serif;
}
a { color: var(--green); }
a:hover { text-decoration: none; }
header.top {
  position: sticky;
  top: 0;
  z-index: 5;
  background: #1c1915;
  color: #f4f1ea;
}
header.top nav {
  max-width: 64rem;
  margin: 0 auto;
  display: flex;
  gap: 0.4rem;
  padding: 0.7rem 1rem;
  overflow-x: auto;
}
header.top a {
  color: #f4f1ea;
  text-decoration: none;
  padding: 0.35rem 0.7rem;
  border-radius: 999px;
  white-space: nowrap;
  font-size: 0.95rem;
}
header.top a.on, header.top a:hover { background: #1b5e45; }
main { max-width: var(--max); margin: 0 auto; padding: 1.4rem 1rem 4rem; }
h1 { font-size: 1.85rem; line-height: 1.2; margin: 0.2rem 0 0.6rem; }
h2 { font-size: 1.35rem; margin: 2rem 0 0.5rem; }
h3 { font-size: 1.05rem; margin: 1.2rem 0 0.3rem; }
.lead { color: var(--muted); margin-top: 0; }
.banner, .card, .q {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 1rem 1.05rem;
  margin: 0.9rem 0;
}
.banner { background: var(--green-soft); border-color: #b7d7c6; }
.warn { background: var(--amber-soft); border-color: #ead7b0; }
ol.steps, ul.clean { margin: 0.3rem 0 0; padding-left: 1.2rem; }
ol.steps li, ul.clean li { margin: 0.28rem 0; }
table { width: 100%; border-collapse: collapse; font-size: 0.95rem; margin: 0.6rem 0; }
th, td { border-bottom: 1px solid var(--line); text-align: left; padding: 0.4rem 0.35rem; vertical-align: top; }
.jump {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin: 0.8rem 0 1.2rem;
}
.jump a {
  width: 2.4rem;
  text-align: center;
  text-decoration: none;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.25rem 0;
  color: var(--ink);
  font-size: 0.9rem;
}
.q { scroll-margin-top: 4.2rem; }
.q h2 { margin: 0; font-size: 1.12rem; }
.qhead { display: flex; gap: 0.7rem; align-items: flex-start; }
.ans {
  flex: 0 0 auto;
  background: var(--green);
  color: white;
  font-weight: 700;
  width: 2.1rem;
  height: 2.1rem;
  border-radius: 8px;
  display: grid;
  place-items: center;
}
.num { color: var(--muted); font-size: 0.85rem; display: block; }
.tag {
  display: inline-block;
  font-size: 0.78rem;
  letter-spacing: 0.02em;
  background: var(--amber-soft);
  color: var(--amber);
  border-radius: 999px;
  padding: 0.05rem 0.45rem;
  margin-bottom: 0.25rem;
}
footer { color: var(--muted); font-size: 0.9rem; margin-top: 2rem; }
code { font-family: Consolas, "Courier New", monospace; font-size: 0.92em; }
.tree { font-family: Consolas, monospace; white-space: pre; background: #f7f4ee; padding: 0.6rem 0.8rem; border-radius: 8px; font-size: 0.9rem; }