:root {
  --bg: #f5f9fa;
  --surface: #ffffff;
  --ink: #17272c;
  --muted: #55696f;
  --primary: #006a80;
  --primary-ink: #ffffff;
  --tint: #d3edf4;
  --line: #d5e0e3;
  --tip: #e6f4ea;
  --tip-line: #7cc08f;
  --warn: #fff4e0;
  --warn-line: #e0a030;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1a1d;
    --surface: #17262a;
    --ink: #e4eef0;
    --muted: #9ab0b6;
    --primary: #5cc8e0;
    --primary-ink: #00252d;
    --tint: #123740;
    --line: #2a3f45;
    --tip: #143323;
    --tip-line: #3d8a58;
    --warn: #3a2c10;
    --warn-line: #b07d20;
  }
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 72px; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.6 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--primary); }
header.top {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; gap: 12px;
  padding: 10px 16px;
  background: var(--surface);
  border-bottom: 1px solid var(--line);
}
header.top strong { font-size: 18px; }
header.top .sub { color: var(--muted); font-size: 14px; }
#menuBtn {
  display: none; margin-left: auto;
  border: 1px solid var(--line); background: var(--bg); color: var(--ink);
  border-radius: 8px; padding: 6px 12px; font: inherit;
}
.layout { display: flex; max-width: 1180px; margin: 0 auto; }
nav.toc {
  flex: 0 0 250px; position: sticky; top: 57px; align-self: flex-start;
  height: calc(100vh - 57px); overflow-y: auto; padding: 20px 12px 40px 16px;
  font-size: 14px;
}
nav.toc h4 { margin: 18px 0 6px; font-size: 12px; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); }
nav.toc a { display: block; padding: 4px 8px; border-radius: 6px; text-decoration: none; color: var(--ink); }
nav.toc a:hover, nav.toc a.on { background: var(--tint); color: var(--primary); }
main { flex: 1; min-width: 0; padding: 20px 20px 80px; }
section { margin-bottom: 56px; }
h1 { font-size: 30px; margin: 8px 0 8px; }
h2 { font-size: 24px; margin: 0 0 6px; padding-top: 8px; border-top: 3px solid var(--primary); }
h3 { font-size: 18px; margin: 28px 0 6px; }
p.lead { font-size: 18px; color: var(--muted); }
.step { display: flex; gap: 24px; align-items: flex-start; margin: 18px 0; }
.step .txt { flex: 1; min-width: 0; }
.step.flip { flex-direction: row-reverse; }
figure { margin: 0; flex: 0 0 240px; }
figure img {
  display: block; width: 240px; height: auto;
  border: 6px solid #1c2428; border-radius: 22px; background: #fff;
  cursor: zoom-in;
}
figcaption { font-size: 13px; color: var(--muted); text-align: center; margin-top: 6px; }
.pair { display: flex; gap: 14px; flex: 0 0 auto; }
.pair figure { flex: 0 0 200px; }
.pair figure img { width: 200px; }
ol, ul { padding-left: 22px; }
li { margin: 4px 0; }
.tip, .warn {
  border-left: 4px solid; border-radius: 6px; padding: 8px 14px; margin: 14px 0;
}
.tip { background: var(--tip); border-color: var(--tip-line); }
.warn { background: var(--warn); border-color: var(--warn-line); }
table { border-collapse: collapse; width: 100%; margin: 12px 0; font-size: 15px; }
th, td { border: 1px solid var(--line); padding: 6px 10px; text-align: left; vertical-align: top; }
th { background: var(--tint); }
kbd, .btn {
  display: inline-block; padding: 0 8px; border: 1px solid var(--primary); color: var(--primary);
  border-radius: 12px; font-size: 14px; font-weight: 600; white-space: nowrap;
}
.btn.fill { background: var(--primary); color: var(--primary-ink); }
#lightbox {
  position: fixed; inset: 0; background: rgba(0,0,0,.85); display: none;
  align-items: center; justify-content: center; z-index: 50; cursor: zoom-out;
}
#lightbox.on { display: flex; }
#lightbox img { max-height: 94vh; max-width: 94vw; border-radius: 16px; }
footer { text-align: center; color: var(--muted); font-size: 13px; padding: 30px 16px; }
@media (max-width: 860px) {
  #menuBtn { display: block; }
  nav.toc {
    display: none; position: fixed; top: 57px; left: 0; right: 0; bottom: 0;
    background: var(--surface); z-index: 9; height: auto;
  }
  nav.toc.open { display: block; }
  .layout { display: block; }
  .step, .step.flip { flex-direction: column; align-items: center; }
  .step .txt { width: 100%; }
  .pair { justify-content: center; }
}
@media print {
  header.top, nav.toc { display: none; }
  section { break-inside: avoid-page; }
}