:root {
  --bg: #f7f7f5;
  --card: #ffffff;
  --ink: #1f2328;
  --muted: #5b6570;
  --line: #e2e5e8;
  --accent: #1f6feb;
  --accent-soft: #e8f1ff;
  --warn: #b45309;
  --ok: #1a7f37;
  --radius: 12px;
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", "Hiragino Sans GB", sans-serif;
  font-size: 17px;
  line-height: 1.75;
}

.wrap {
  max-width: 760px;
  margin: 0 auto;
  padding: 16px 16px 64px;
}

a { color: var(--accent); }

.topbar {
  background: var(--card);
  border-bottom: 1px solid var(--line);
  padding: 10px 16px;
  display: flex;
  flex-wrap: wrap;
  gap: 8px 14px;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 5;
}

.brand { font-weight: 700; color: var(--ink); text-decoration: none; }

.topnav { display: flex; gap: 14px; font-size: 15px; }
.topnav a { text-decoration: none; }
.topnav a:hover { text-decoration: underline; }

h1 { font-size: 1.45rem; line-height: 1.45; margin: 8px 0 6px; }
h2 { font-size: 1.18rem; margin: 26px 0 8px; }
h3 { font-size: 1.05rem; margin: 18px 0 6px; }

.unit-meta, .u-meta, .crumb, .hint {
  color: var(--muted);
  font-size: 14px;
  margin: 4px 0 10px;
}

.blk {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin: 14px 0;
}

.blk > h2:first-child { margin-top: 0; }

.blk p, .blk li { overflow-wrap: anywhere; }

blockquote {
  margin: 10px 0;
  padding: 8px 12px;
  background: #fbfaf7;
  border-left: 3px solid #d9d2c5;
  color: #444;
  font-size: 15.5px;
}

pre {
  background: #f4f5f7;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  overflow-x: auto;
  font-size: 14.5px;
  line-height: 1.6;
}

code { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }

.modebar {
  display: flex;
  gap: 8px;
  margin: 14px 0 4px;
  flex-wrap: wrap;
}

.btn, .mode-btn {
  display: inline-block;
  min-height: 40px;
  padding: 8px 14px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--card);
  color: var(--ink);
  font-size: 15px;
  text-decoration: none;
  cursor: pointer;
  line-height: 1.5;
}

.btn.small, .mode-btn { min-height: 36px; padding: 6px 12px; font-size: 14px; }

.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.big { font-size: 16px; padding: 10px 18px; }

.mode-btn.active { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); font-weight: 600; }

.quick { display: flex; gap: 8px; flex-wrap: wrap; margin: 12px 0; }

.stats {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin: 12px 0 0;
  font-size: 14.5px;
  color: var(--muted);
}

.stats b { color: var(--ink); }

.units { list-style: none; padding: 0; margin: 12px 0; }

.unit-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
  margin: 10px 0;
}

.u-n { color: var(--muted); font-size: 13.5px; }
.unit-card h3 { margin: 2px 0 6px; font-size: 1.05rem; }
.unit-card h3 a { text-decoration: none; }
.u-modes { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 8px; }
.badge { display: inline-block; font-size: 13px; padding: 1px 8px; border-radius: 999px; border: 1px solid var(--line); color: var(--muted); }
.badge.done { color: var(--ok); border-color: #b7e0c2; background: #eef9f1; }
.badge.todo { color: var(--warn); border-color: #ecd9b7; background: #fdf6ea; }

.q { border-top: 1px dashed var(--line); padding: 12px 0 4px; }
.q:first-of-type { border-top: 0; }
.q-n { font-size: 13.5px; color: var(--muted); }
.q-t { margin: 4px 0 8px; font-weight: 600; }
.q-act { display: flex; gap: 8px; flex-wrap: wrap; }
.q-ans { margin: 10px 0 4px; padding: 10px 12px; background: #fbfaf7; border: 1px solid #e6e0d2; border-radius: 8px; font-size: 15.5px; }
.q-ans .label { display: block; font-size: 13px; color: var(--warn); margin-bottom: 4px; }
.q-state { font-size: 13.5px; color: var(--muted); margin: 6px 0 0; }

textarea.prod {
  width: 100%;
  min-height: 140px;
  font-size: 16px;
  font-family: inherit;
  line-height: 1.7;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  color: var(--ink);
}

.marks { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; margin: 16px 0; }
.mark-state { font-size: 14px; color: var(--muted); }

.unit-foot { display: flex; gap: 10px; justify-content: space-between; margin: 22px 0 8px; }

.note {
  background: #fbfaf7;
  border: 1px solid #e6e0d2;
  border-radius: var(--radius);
  padding: 12px 14px;
  font-size: 14.5px;
  color: #4a4438;
}

footer.foot { color: var(--muted); font-size: 13.5px; text-align: center; padding: 24px 0 0; }

@media (max-width: 400px) {
  body { font-size: 16px; }
  h1 { font-size: 1.3rem; }
  .btn, .mode-btn { padding: 8px 12px; }
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16181c;
    --card: #1e2126;
    --ink: #e6e8ea;
    --muted: #9aa4af;
    --line: #33383f;
    --accent: #6ea8ff;
    --accent-soft: #1c2b47;
    --warn: #e3b341;
    --ok: #56d364;
  }
  pre { background: #14171b; }
  .q-ans, .note, blockquote { background: #20242a; border-color: #383c42; }
  textarea.prod { background: #14171b; }
}