:root {
  --bg: #f5f6f8;
  --panel: #ffffff;
  --panel-alt: #eef1f5;
  --border: #dde2e9;
  --ink: #1b2430;
  --ink-dim: #5b6676;
  --ink-faint: #8993a4;
  --accent: #2f6feb;
  --accent-ink: #0b3f9e;
  --accent-soft: #e4edfc;
  --loop: #0f8a65;
  --loop-soft: #e2f5ee;
  --eval: #b3690a;
  --eval-soft: #fbedda;
  --shadow: 0 1px 2px rgba(20, 24, 34, 0.04), 0 8px 24px rgba(20, 24, 34, 0.06);

  --tok-kw: #a626a4;
  --tok-str: #3c9a40;
  --tok-com: #8b93a3;
  --tok-num: #986801;
  --tok-dec: #4078f2;
  --tok-builtin: #0b739e;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #10121a;
    --panel: #171a22;
    --panel-alt: #1d212b;
    --border: #2a2f3b;
    --ink: #e4e7ec;
    --ink-dim: #969fb0;
    --ink-faint: #666f80;
    --accent: #6ea8fe;
    --accent-ink: #cfe0ff;
    --accent-soft: #1b2c4a;
    --loop: #4fd8ab;
    --loop-soft: #103226;
    --eval: #e0a855;
    --eval-soft: #3a2a12;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px rgba(0, 0, 0, 0.35);

    --tok-kw: #c678dd;
    --tok-str: #98c379;
    --tok-com: #5c6370;
    --tok-num: #d19a66;
    --tok-dec: #61afef;
    --tok-builtin: #56b6c2;
  }
}

:root[data-theme="light"] {
  --bg: #f5f6f8; --panel: #ffffff; --panel-alt: #eef1f5; --border: #dde2e9;
  --ink: #1b2430; --ink-dim: #5b6676; --ink-faint: #8993a4;
  --accent: #2f6feb; --accent-ink: #0b3f9e; --accent-soft: #e4edfc;
  --loop: #0f8a65; --loop-soft: #e2f5ee; --eval: #b3690a; --eval-soft: #fbedda;
}
:root[data-theme="dark"] {
  --bg: #10121a; --panel: #171a22; --panel-alt: #1d212b; --border: #2a2f3b;
  --ink: #e4e7ec; --ink-dim: #969fb0; --ink-faint: #666f80;
  --accent: #6ea8fe; --accent-ink: #cfe0ff; --accent-soft: #1b2c4a;
  --loop: #4fd8ab; --loop-soft: #103226; --eval: #e0a855; --eval-soft: #3a2a12;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}
.mono, code, pre {
  font-family: ui-monospace, "SF Mono", "Cascadia Code", "JetBrains Mono", Menlo, Consolas, monospace;
}

.page { max-width: 1240px; margin: 0 auto; padding: 48px 28px 80px; }

/* ---------- Hero ---------- */
.hero { max-width: 680px; margin-bottom: 36px; }
.hero-kicker {
  font-size: 12.5px; font-weight: 600; letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--ink-faint);
}
.hero h1 { font-size: 36px; margin: 6px 0 14px; letter-spacing: -0.01em; }
.hero h1 .mono { font-weight: 700; }
.hero-sub { color: var(--ink-dim); font-size: 15.5px; margin: 0; }
.hero-hint {
  background: var(--accent-soft); color: var(--accent-ink);
  padding: 1px 6px; border-radius: 5px; font-weight: 600;
}

/* ---------- Layout ---------- */
.layout { display: flex; gap: 28px; align-items: flex-start; }
.diagram { flex: 0 0 600px; min-width: 0; display: flex; flex-direction: column; gap: 0; }
.drilldown {
  flex: 1 1 380px; min-width: 320px; position: sticky; top: 24px;
  background: var(--panel); border: 1px solid var(--border); border-radius: 14px;
  box-shadow: var(--shadow); max-height: calc(100vh - 48px); display: flex; flex-direction: column;
}
@media (max-width: 980px) {
  .layout { flex-direction: column; }
  .diagram { flex: 1 1 auto; width: 100%; }
  .drilldown { position: static; width: 100%; max-height: none; }
}

.drilldown-head {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 16px; border-bottom: 1px solid var(--border); flex: 0 0 auto;
}
.drilldown-title { font-weight: 700; font-size: 13.5px; }
.drilldown-reset {
  font-size: 12.5px; color: var(--ink-faint); cursor: pointer; user-select: none;
  padding: 3px 8px; border-radius: 6px;
}
.drilldown-reset:hover { background: var(--panel-alt); color: var(--ink); }
.drilldown-reset.hidden { visibility: hidden; }

.drill-track {
  display: flex; gap: 12px; padding: 14px; overflow-x: auto; overflow-y: hidden;
  flex: 1 1 auto; align-items: flex-start;
}
.drill-empty {
  color: var(--ink-dim); font-size: 13.5px; padding: 8px 4px; max-width: 320px;
}
.drill-empty code { background: var(--panel-alt); padding: 1px 5px; border-radius: 4px; font-size: 12.5px; }

.drill-card {
  flex: 0 0 310px; background: var(--panel-alt); border: 1px solid var(--border);
  border-radius: 11px; overflow: hidden; display: flex; flex-direction: column;
  animation: slide-in 0.16s ease-out;
}
@keyframes slide-in { from { opacity: 0; transform: translateX(6px); } to { opacity: 1; transform: none; } }

.drill-card-head { padding: 11px 13px 9px; border-bottom: 1px solid var(--border); }
.drill-card-row { display: flex; align-items: flex-start; justify-content: space-between; gap: 8px; }
.drill-card-kind {
  font-size: 10.5px; text-transform: uppercase; letter-spacing: 0.06em; font-weight: 700;
  color: var(--accent-ink); background: var(--accent-soft); padding: 2px 6px; border-radius: 5px;
  display: inline-block; margin-bottom: 5px;
}
.drill-card-name { font-weight: 700; font-size: 14.5px; }
.drill-card-loc { color: var(--ink-faint); font-size: 11.5px; margin-top: 3px; }
.drill-card-close {
  cursor: pointer; color: var(--ink-faint); font-size: 16px; line-height: 1; padding: 2px 4px;
  border-radius: 5px; flex: 0 0 auto;
}
.drill-card-close:hover { background: var(--panel); color: var(--ink); }
.drill-card-blurb { font-size: 12.5px; color: var(--ink-dim); margin: 7px 0 0; }
.drill-card-code {
  padding: 11px 13px; overflow: auto; font-size: 12.5px; flex: 1 1 auto;
}
.drill-card-code pre { margin: 0; white-space: pre; }

/* ---------- Diagram: steps ---------- */
.step {
  background: var(--panel); border: 1px solid var(--border); border-radius: 14px;
  box-shadow: var(--shadow); margin-bottom: 0;
  position: relative;
}
.step + .step { margin-top: 22px; }
.connector {
  width: 2px; height: 22px; background: var(--border); margin: 0 auto; margin-left: 29px;
}

.step-head {
  display: flex; align-items: center; gap: 13px; padding: 15px 18px; cursor: pointer; user-select: none;
}
.step-badge {
  flex: 0 0 auto; width: 32px; height: 32px; border-radius: 9px; background: var(--accent-soft);
  color: var(--accent-ink); display: flex; align-items: center; justify-content: center;
  font-weight: 700; font-size: 13.5px;
}
.step.is-loop .step-badge { background: var(--loop-soft); color: var(--loop); }
.step-titles { flex: 1 1 auto; min-width: 0; }
.step-title { font-weight: 700; font-size: 15.5px; }
.step-subtitle { color: var(--ink-dim); font-size: 12.5px; margin-top: 1px; }
.step-chevron {
  flex: 0 0 auto; width: 20px; height: 20px; color: var(--ink-faint);
  transition: transform 0.15s ease;
}
.step.open > .step-head .step-chevron { transform: rotate(90deg); }

.step-body { display: none; padding: 0 18px 18px; }
.step.open > .step-body { display: block; }

.step-code { background: var(--panel-alt); border: 1px solid var(--border); border-radius: 10px; padding: 13px 15px; overflow: auto; }
.step-code pre { margin: 0; font-size: 13px; white-space: pre; }

/* sub-steps inside the loop */
.loop-wrap { margin-top: 2px; }
.loop-frame {
  border: 1.5px dashed var(--border); border-radius: 12px; padding: 14px 14px 18px; margin-top: 2px;
  background: color-mix(in srgb, var(--loop-soft) 35%, transparent);
}
.loop-frame-label {
  font-size: 11px; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em;
  color: var(--loop); margin-bottom: 10px;
}
.substep { background: var(--panel); border: 1px solid var(--border); border-radius: 10px; }
.substep + .substep { margin-top: 10px; }
.substep .step-head { padding: 11px 14px; gap: 11px; }
.substep .step-badge { width: 26px; height: 26px; font-size: 11.5px; border-radius: 7px; }
.substep .step-title { font-size: 14px; }
.substep .step-subtitle { font-size: 11.5px; }
.substep .step-body { padding: 0 14px 14px; }
.substep[data-sub="step3e"] .step-badge { background: var(--eval-soft); color: var(--eval); }

.loop-back {
  display: flex; align-items: center; gap: 8px; margin-top: 12px; padding-left: 2px;
  color: var(--loop); font-size: 11.5px; font-weight: 600;
}
.loop-back svg { flex: 0 0 auto; }

/* ---------- Code tokens ---------- */
pre.code, .step-code pre, .drill-card-code pre, .ref-code pre { line-height: 1.55; }
.tok-kw { color: var(--tok-kw); font-weight: 600; }
.tok-str { color: var(--tok-str); }
.tok-com { color: var(--tok-com); font-style: italic; }
.tok-num { color: var(--tok-num); }
.tok-dec { color: var(--tok-dec); }
.tok-builtin { color: var(--tok-builtin); }
.sym-link {
  color: var(--accent-ink); background: var(--accent-soft); border-radius: 4px; padding: 0 2px;
  cursor: pointer; text-decoration: none; border-bottom: 1.5px dotted var(--accent);
}
.sym-link:hover { background: var(--accent); color: #fff; border-bottom-color: transparent; }

/* ---------- Reference ---------- */
.reference { margin-top: 56px; max-width: 900px; }
.reference h2 { font-size: 20px; margin-bottom: 4px; }
.reference-sub { color: var(--ink-dim); font-size: 13.5px; margin: 0 0 18px; }

.ref-file {
  border: 1px solid var(--border); border-radius: 12px; margin-bottom: 12px; overflow: hidden;
  background: var(--panel);
}
.ref-file-head {
  display: flex; align-items: center; justify-content: space-between; gap: 10px;
  padding: 13px 16px; cursor: pointer; user-select: none;
}
.ref-file-name { font-weight: 700; font-size: 14px; }
.ref-file-meta { color: var(--ink-faint); font-size: 12px; }
.ref-file-chevron { color: var(--ink-faint); width: 18px; height: 18px; transition: transform 0.15s ease; }
.ref-file.open .ref-file-chevron { transform: rotate(90deg); }
.ref-file-body { display: none; border-top: 1px solid var(--border); }
.ref-file.open .ref-file-body { display: block; }

.ref-code { overflow: auto; max-height: 520px; background: var(--panel-alt); }
.ref-code table { border-collapse: collapse; width: 100%; font-size: 12.5px; }
.ref-code td { padding: 0 10px; vertical-align: top; white-space: pre; }
.ref-code td.ln {
  color: var(--ink-faint); text-align: right; user-select: none; width: 1%;
  border-right: 1px solid var(--border); padding-right: 10px;
}
.ref-code td.src { padding-left: 14px; width: 100%; }

/* ---------- Footer ---------- */
.page-footer { margin-top: 56px; color: var(--ink-faint); font-size: 12px; border-top: 1px solid var(--border); padding-top: 16px; }