:root {
    --bg: #edf1ea;
    --surface: #f8faf6;
    --surface-line: #dfe6da;
    --ink: #17211e;
    --ink-soft: #4b564f;
    --ink-faint: #7c8880;
    --line: #c9d0c7;
    --direct: #2f6f5e;
    --direct-bg: #e1eee9;
    --tunnel: #a5561e;
    --tunnel-bg: #f5e6d9;
    --code-bg: #e7ece4;
    --code-ink: #24322c;
    --shadow: 0 1px 2px rgba(23, 33, 30, 0.06);
  }

  :root[data-theme="dark"] {
    --bg: #10161a;
    --surface: #161f24;
    --surface-line: #23302f;
    --ink: #e7eee9;
    --ink-soft: #a9b7ae;
    --ink-faint: #728077;
    --line: #2b3a38;
    --direct: #62c2a2;
    --direct-bg: rgba(98, 194, 162, 0.13);
    --tunnel: #e3985c;
    --tunnel-bg: rgba(227, 152, 92, 0.13);
    --code-bg: #1c2b28;
    --code-ink: #d9e6df;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.35);
  }

  @media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
      --bg: #10161a;
      --surface: #161f24;
      --surface-line: #23302f;
      --ink: #e7eee9;
      --ink-soft: #a9b7ae;
      --ink-faint: #728077;
      --line: #2b3a38;
      --direct: #62c2a2;
      --direct-bg: rgba(98, 194, 162, 0.13);
      --tunnel: #e3985c;
      --tunnel-bg: rgba(227, 152, 92, 0.13);
      --code-bg: #1c2b28;
      --code-ink: #d9e6df;
      --shadow: 0 1px 3px rgba(0, 0, 0, 0.35);
    }
  }

  * { box-sizing: border-box; }

  body {
    margin: 0;
    background: var(--bg);
    color: var(--ink);
    font-family: -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
  }

  .mono {
    font-family: ui-monospace, "SF Mono", "Cascadia Code", "Consolas", "Liberation Mono", monospace;
  }

  .wrap {
    max-width: 760px;
    margin: 0 auto;
    padding: 3.2rem 1.5rem 5rem;
  }

  header.top {
    margin-bottom: 2.6rem;
  }

  .eyebrow {
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    font-size: 0.74rem;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--ink-faint);
    margin: 0 0 0.9rem;
  }

  h1 {
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    font-size: clamp(1.6rem, 4vw, 2.15rem);
    font-weight: 600;
    letter-spacing: -0.01em;
    text-wrap: balance;
    margin: 0 0 0.9rem;
    color: var(--ink);
  }

  .lede {
    max-width: 62ch;
    color: var(--ink-soft);
    font-size: 1.03rem;
    margin: 0;
  }

  .lede strong { color: var(--ink); font-weight: 600; }

  /* lane diagram */
  .lanes {
    margin: 2.2rem 0 2.6rem;
    border: 1px solid var(--line);
    border-radius: 10px;
    overflow: hidden;
    background: var(--surface);
    box-shadow: var(--shadow);
  }

  .lane-row {
    display: grid;
    grid-template-columns: 7.5rem 1fr;
    align-items: stretch;
    border-bottom: 1px solid var(--line);
  }
  .lane-row:last-child { border-bottom: none; }

  .lane-tag {
    display: flex;
    align-items: center;
    padding: 0.85rem 1rem;
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    font-size: 0.72rem;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink-faint);
    border-right: 1px solid var(--line);
  }

  .lane-body {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    flex-wrap: wrap;
    padding: 0.85rem 1.1rem;
    font-size: 0.92rem;
  }

  .chip {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.22rem 0.6rem;
    border-radius: 999px;
    font-size: 0.82rem;
    font-weight: 600;
    white-space: nowrap;
  }
  .chip.direct { background: var(--direct-bg); color: var(--direct); }
  .chip.tunnel { background: var(--tunnel-bg); color: var(--tunnel); }

  .arrow { color: var(--ink-faint); font-size: 0.95rem; }

  /* section headings */
  h2 {
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    font-size: 1.05rem;
    font-weight: 600;
    margin: 0;
    color: var(--ink);
  }

  section.explain {
    margin-bottom: 2.6rem;
  }
  section.explain p { margin: 0 0 0.9rem; color: var(--ink-soft); }
  section.explain p:last-child { margin-bottom: 0; }

  .app-list {
    display: flex;
    flex-direction: column;
    gap: 1.4rem;
    margin-bottom: 2.6rem;
  }

  .app-card {
    background: var(--surface);
    border: 1px solid var(--surface-line);
    border-radius: 12px;
    padding: 1.4rem 1.5rem 1.6rem;
    box-shadow: var(--shadow);
  }

  .app-card > header {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    gap: 0.8rem;
    margin-bottom: 1.1rem;
    padding-bottom: 0.9rem;
    border-bottom: 1px solid var(--surface-line);
  }

  .app-card > header .note {
    font-size: 0.78rem;
    color: var(--ink-faint);
  }

  ol.steps {
    margin: 0;
    padding: 0;
    list-style: none;
    counter-reset: step;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
  }

  ol.steps li {
    counter-increment: step;
    display: grid;
    grid-template-columns: 1.6rem 1fr;
    gap: 0.7rem;
    font-size: 0.95rem;
  }

  ol.steps li > span {
    min-width: 0;
  }

  ol.steps li::before {
    content: counter(step);
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    font-size: 0.78rem;
    font-weight: 700;
    color: var(--ink-faint);
    border: 1px solid var(--line);
    border-radius: 50%;
    width: 1.6rem;
    height: 1.6rem;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
  }

  code, .rule {
    font-family: ui-monospace, "SF Mono", Consolas, monospace;
    background: var(--code-bg);
    color: var(--code-ink);
    padding: 0.12rem 0.42rem;
    border-radius: 5px;
    font-size: 0.86rem;
    word-break: break-word;
  }

  .shortcut {
    margin-top: 1.1rem;
    padding-top: 1rem;
    border-top: 1px dashed var(--surface-line);
    font-size: 0.88rem;
    color: var(--ink-soft);
  }
  .shortcut a { color: var(--direct); text-decoration: none; border-bottom: 1px solid currentColor; }
  .shortcut a:hover { opacity: 0.8; }
  .shortcut a:focus-visible { outline: 2px solid var(--direct); outline-offset: 2px; border-radius: 2px; }

  .callout {
    background: var(--surface);
    border: 1px solid var(--surface-line);
    border-left: 3px solid var(--direct);
    border-radius: 0 10px 10px 0;
    padding: 1.2rem 1.4rem;
    margin-bottom: 2.4rem;
    box-shadow: var(--shadow);
  }
  .callout h2 { margin-bottom: 0.55rem; }
  .callout p { margin: 0; color: var(--ink-soft); font-size: 0.95rem; }
  .callout a { color: var(--ink); }
  .callout a:focus-visible { outline: 2px solid var(--direct); outline-offset: 2px; }

  footer.foot {
    padding-top: 1.6rem;
    border-top: 1px solid var(--line);
    font-size: 0.82rem;
    color: var(--ink-faint);
  }
  footer.foot p { margin: 0 0 0.5rem; }

  @media (max-width: 520px) {
    .lane-row { grid-template-columns: 1fr; }
    .lane-tag { border-right: none; border-bottom: 1px solid var(--line); padding-bottom: 0.5rem; }
    ol.steps li { grid-template-columns: 1.4rem 1fr; font-size: 0.92rem; }
  }

/* cross-page nav */
.crumb {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  font-family: ui-monospace, "SF Mono", Consolas, monospace;
  font-size: 0.78rem;
  color: var(--ink-faint);
  margin-bottom: 2.2rem;
  flex-wrap: wrap;
}
.crumb a {
  color: var(--ink-soft);
  text-decoration: none;
  border-bottom: 1px solid var(--line);
}
.crumb a:hover { color: var(--direct); border-color: currentColor; }
.crumb a:focus-visible { outline: 2px solid var(--direct); outline-offset: 2px; }

/* platform list */
.platforms {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 0.7rem;
  margin: 1rem 0 0;
}
.platform {
  border: 1px solid var(--surface-line);
  background: var(--surface);
  border-radius: 10px;
  padding: 0.8rem 1rem;
  font-size: 0.88rem;
}
.platform b { display: block; font-size: 0.75rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--ink-faint); margin-bottom: 0.3rem; font-family: ui-monospace, "SF Mono", Consolas, monospace; }

.tip {
  font-size: 0.86rem;
  color: var(--ink-soft);
  background: var(--code-bg);
  border-radius: 8px;
  padding: 0.7rem 0.9rem;
  margin-top: 1rem;
}
.tip b { color: var(--ink); }