:root {
  --bg: #fff; --bg-elev: #f7faf9; --bg-soft: #edf7f4; --border: #d9e5e1;
  --text: #17221f; --text-mute: #5d6c67; --text-dim: #92a09b;
  --accent: #087f68; --accent-dark: #05604f; --accent-soft: #dcf4ed;
  --cyan: #087da3; --amber: #c56a09; --green: #16844d; --red: #cf3e51;
  --code-bg: #eff5f3; --mono: "SF Mono", Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", sans-serif;
}
html { box-sizing: border-box; } *, *::before, *::after { box-sizing: inherit; }
body { margin: 0; color: var(--text); background: var(--bg); font-family: var(--sans); font-size: 16px; line-height: 1.66; }
main { max-width: 880px; margin: 0 auto; padding: 32px 28px 120px; }
.topnav { position: sticky; top: 0; z-index: 20; border-bottom: 1px solid var(--border); background: rgba(255,255,255,.92); backdrop-filter: saturate(180%) blur(12px); }
.topnav .inner { max-width: 1120px; margin: 0 auto; padding: 11px 28px; display: flex; align-items: center; gap: 14px; font-size: 13px; }
.crumb { color: var(--text-mute); } .crumb-link { color: var(--accent); text-decoration: none; } .crumb-link:hover { text-decoration: underline; }
.step-pill { margin-left: auto; border: 1px solid var(--border); border-radius: 999px; padding: 3px 10px; color: var(--text-mute); font-family: var(--mono); font-size: 11px; white-space: nowrap; }
h1 { margin: 17px 0 5px; font-size: clamp(29px,5vw,40px); line-height: 1.13; font-weight: 680; letter-spacing: -.025em; }
h1 + .subtitle { margin: 0 0 28px; color: var(--text-mute); font-size: 17px; max-width: 790px; }
h2 { margin: 40px 0 11px; padding-bottom: 6px; border-bottom: 1px solid var(--border); font-size: 21px; line-height: 1.35; font-weight: 630; letter-spacing: -.008em; }
h3 { margin: 26px 0 8px; font-size: 17px; font-weight: 650; }
h4 { margin: 20px 0 6px; font-size: 15px; font-weight: 650; }
p { margin: 10px 0; } a { color: var(--accent); text-decoration: none; } a:hover { text-decoration: underline; } strong { font-weight: 650; }
ul, ol { padding-left: 23px; } li { margin: 5px 0; }
blockquote { margin: 16px 0; padding: 4px 16px; border-left: 3px solid var(--border); color: var(--text-mute); }
details { margin: 14px 0; padding: 10px 14px; border: 1px solid var(--border); border-radius: 8px; background: var(--bg-elev); }
summary { cursor: pointer; color: var(--accent-dark); font-weight: 620; }
details[open] summary { margin-bottom: 8px; }
code { padding: 1px 5px; border: 1px solid var(--border); border-radius: 4px; background: var(--code-bg); font: 13.5px var(--mono); }
pre { margin: 14px 0; padding: 14px 16px; overflow-x: auto; border: 1px solid var(--border); border-radius: 8px; background: var(--code-bg); font: 13px/1.55 var(--mono); }
pre code { padding: 0; border: 0; background: transparent; }
.math { font-family: "STIX Two Math", "Latin Modern Math", Cambria, Georgia, serif; font-style: italic; font-size: 1.04em; }
.math.block { display: block; margin: 17px 0; padding: 13px 10px; border: 1px solid var(--border); border-radius: 8px; background: var(--bg-elev); text-align: center; font-size: 1.08em; overflow-x: auto; }
table { width: 100%; margin: 15px 0; border-collapse: collapse; font-size: 14px; }
th, td { padding: 8px 10px; border-bottom: 1px solid var(--border); text-align: left; vertical-align: top; }
th { color: var(--text-mute); font: 600 11px var(--mono); letter-spacing: .06em; text-transform: uppercase; } tr:hover td { background: var(--bg-elev); }
.callout { margin: 17px 0; padding: 12px 16px; border: 1px solid var(--border); border-left: 3px solid var(--accent); border-radius: 4px 8px 8px 4px; background: var(--bg-elev); }
.callout.warn { border-left-color: var(--amber); } .callout.ok { border-left-color: var(--green); } .callout.bad { border-left-color: var(--red); }
.callout .label { margin-bottom: 3px; color: var(--text-mute); font: 10px var(--mono); letter-spacing: .09em; text-transform: uppercase; }
.topic-grid { display: grid; grid-template-columns: repeat(auto-fit,minmax(200px,1fr)); gap: 10px; margin: 16px 0; }
.topic-card { min-height: 88px; padding: 12px 14px; border: 1px solid var(--border); border-radius: 9px; background: var(--bg-elev); }
.topic-card .k { color: var(--accent); font: 10px var(--mono); letter-spacing: .07em; text-transform: uppercase; }
.topic-card .v { margin-top: 3px; font-weight: 620; line-height: 1.45; } .topic-card .s { margin-top: 4px; color: var(--text-mute); font-size: 13px; line-height: 1.45; }
.toc-grid { display: grid; gap: 11px; margin: 23px 0; }
.toc-card { display: flex; gap: 16px; align-items: flex-start; padding: 16px 18px; border: 1px solid var(--border); border-radius: 10px; background: var(--bg-elev); color: inherit; transition: transform .14s ease,border-color .14s ease,box-shadow .14s ease; }
.toc-card:hover { transform: translateY(-1px); border-color: #74b9a9; box-shadow: 0 8px 24px rgba(8,90,70,.08); text-decoration: none; }
.toc-card .num { flex: 0 0 34px; color: var(--text-dim); font: 21px var(--mono); } .toc-card .ttl { margin-bottom: 3px; font-size: 16px; font-weight: 650; }
.toc-card .sum { color: var(--text-mute); font-size: 14px; line-height: 1.48; }
.hero-loop { position: relative; margin: 24px 0 30px; padding: 22px; overflow: hidden; border: 1px solid #cde4dd; border-radius: 14px; background: radial-gradient(circle at 90% 8%,rgba(8,127,104,.16),transparent 31%),linear-gradient(145deg,#fbfffd,#f0f8f6); }
.hero-loop::after { content: ""; position: absolute; width: 170px; height: 170px; right: -72px; bottom: -100px; border: 34px solid rgba(8,125,163,.08); border-radius: 50%; }
.loop-row { position: relative; z-index: 1; display: grid; grid-template-columns: repeat(4,1fr); gap: 8px; align-items: center; }
.loop-node { padding: 12px 9px; border: 1px solid var(--border); border-radius: 9px; background: rgba(255,255,255,.9); text-align: center; }
.loop-node b { display: block; color: var(--accent); font: 12px var(--mono); } .loop-node span { color: var(--text-mute); font-size: 12px; }
.pipeline { margin: 16px 0; padding: 14px; overflow-x: auto; border: 1px solid var(--border); border-radius: 8px; background: var(--code-bg); font: 12.5px/1.55 var(--mono); white-space: pre; }
.chips { display: flex; flex-wrap: wrap; gap: 6px; margin: 12px 0; } .chip { padding: 2px 8px; border: 1px solid var(--border); border-radius: 999px; background: var(--code-bg); color: var(--text-mute); font: 10px var(--mono); }
.prompt-list li { margin: 9px 0; } .prompt-list em { color: var(--text-mute); }
.sources { color: var(--text-mute); font-size: 14px; } .sources li { margin: 8px 0; }
footer.lesson-nav { display: flex; justify-content: space-between; gap: 12px; margin-top: 60px; padding-top: 20px; border-top: 1px solid var(--border); font-size: 14px; }
.lesson-nav a { display: inline-flex; flex: 1; max-width: 49%; flex-direction: column; gap: 2px; padding: 10px 14px; border: 1px solid var(--border); border-radius: 8px; }
.lesson-nav a:hover { background: var(--bg-elev); text-decoration: none; } .lesson-nav a.next { align-items: flex-end; text-align: right; }
.lesson-nav .dir { color: var(--text-mute); font: 10px var(--mono); letter-spacing: .08em; text-transform: uppercase; } .lesson-nav .ttl { color: var(--accent); }

/* ---- "you are here" linear spine (7 pipeline stages = 7 lessons) ---- */
.spine { display: flex; flex-wrap: wrap; gap: 4px; margin: 18px 0 26px; padding: 8px; border: 1px solid var(--border); border-radius: 10px; background: var(--bg-elev); }
.spine .seg { flex: 1 1 0; min-width: 84px; padding: 6px 6px; border-radius: 7px; color: var(--text-dim); background: var(--bg); border: 1px solid var(--border); text-align: center; font: 11px/1.25 var(--mono); text-decoration: none; }
.spine a.seg:hover { border-color: #74b9a9; color: var(--accent-dark); }
.spine .seg small { display: block; font-size: 9px; letter-spacing: .05em; text-transform: uppercase; opacity: .7; margin-bottom: 1px; }
.spine .seg.done { color: var(--text-mute); }
.spine .seg.here { color: #fff; background: var(--accent); border-color: var(--accent); font-weight: 650; }
.spine .seg.here small { opacity: .85; }

/* ---- interactive widgets (ported from sibling tracks to this one) ---- */
.widget { background: var(--bg-elev); border: 1px solid var(--border); border-radius: 10px; padding: 18px; margin: 24px 0; }
.widget .title { font-weight: 640; font-size: 14px; color: var(--text); margin-bottom: 4px; }
.widget .hint { font-size: 13px; color: var(--text-mute); line-height: 1.55; margin-bottom: 14px; }
.widget .hint b, .widget .hint strong { color: var(--text); }
.widget .controls { display: flex; flex-wrap: wrap; gap: 10px 16px; align-items: center; margin: 10px 0 12px; }
.widget canvas { width: 100%; display: block; background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px; }
button { font-family: var(--sans); font-size: 13px; background: var(--bg-soft); color: var(--text); border: 1px solid var(--border); padding: 6px 12px; border-radius: 6px; cursor: pointer; transition: background .12s ease, border-color .12s ease; }
button:hover { background: var(--accent-soft); border-color: #74b9a9; }
button.primary { background: var(--accent); color: #fff; border-color: var(--accent); font-weight: 640; }
button.primary:hover { background: var(--accent-dark); }
button[aria-pressed="true"] { background: var(--accent-soft); border-color: var(--accent); color: var(--accent-dark); font-weight: 640; }
button:disabled { opacity: .45; cursor: not-allowed; }
input[type="range"] { -webkit-appearance: none; appearance: none; height: 4px; background: var(--border); border-radius: 4px; outline: none; width: 200px; max-width: min(220px,44vw); accent-color: var(--accent); }
input[type="range"]::-webkit-slider-thumb { -webkit-appearance: none; appearance: none; width: 14px; height: 14px; background: var(--accent); border-radius: 50%; cursor: pointer; border: none; }
input[type="range"]::-moz-range-thumb { width: 14px; height: 14px; background: var(--accent); border-radius: 50%; cursor: pointer; border: none; }
input[type="text"], input[type="number"] { background: var(--code-bg); border: 1px solid var(--border); color: var(--text); border-radius: 6px; padding: 5px 8px; font-family: var(--mono); font-size: 13px; }
select { font-family: var(--sans); font-size: 13px; background: var(--bg-soft); color: var(--text); border: 1px solid var(--border); border-radius: 6px; padding: 5px 8px; cursor: pointer; }
label.inline { font-size: 13px; color: var(--text-mute); display: inline-flex; align-items: center; flex-wrap: wrap; gap: 8px; max-width: 100%; }
label.inline .val { font-family: var(--mono); color: var(--text); min-width: 40px; display: inline-block; }
.kpi-grid { display: grid; grid-template-columns: repeat(auto-fit,minmax(140px,1fr)); gap: 8px; margin: 12px 0; }
.kpi { background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px; padding: 10px 12px; }
.kpi .k { font-size: 11px; color: var(--text-mute); font-family: var(--mono); text-transform: uppercase; letter-spacing: .06em; line-height: 1.3; }
.kpi .v { font-size: 18px; font-family: var(--mono); margin-top: 3px; }
.kpi.flag .v { color: var(--red); } .kpi.good .v { color: var(--green); }
.widget details { margin-top: 12px; background: var(--bg); }
.widget summary { cursor: pointer; color: var(--text-mute); font-size: 13px; font-weight: 500; }
@media (max-width:640px) { main { padding: 23px 18px 80px; } .topnav .inner { flex-wrap: wrap; gap: 7px; padding: 9px 18px; } .step-pill { width: 100%; margin-left: 0; } .loop-row { grid-template-columns: 1fr 1fr; } footer.lesson-nav { flex-direction: column; } .lesson-nav a { max-width: none; } .lesson-nav a.next { align-items: flex-start; text-align: left; } table { display: block; overflow-x: auto; } :not(pre) > code { overflow-wrap: anywhere; word-break: break-word; } }
@media (prefers-reduced-motion:reduce) { *,*::before,*::after { transition: none !important; } }