:root {
  color-scheme: light;
  --bg: #fff; --surface: #f7f9fa; --ink: #101214; --muted: #37414a;
  --line: #d5dce1; --line-strong: #69737c; --accent: #1b1f23;
  --p: #2b6b4d; --e: #2f5f88; --s: #95542f; --c: #625087;
  --header: rgba(255,255,255,.95); --max: 1120px;
}
html[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0d1013; --surface: #15191d; --ink: #f4f6f8; --muted: #bcc4cb;
  --line: #303840; --line-strong: #69737c; --accent: #e2e7eb;
  --p: #72b28e; --e: #83abd0; --s: #d09168; --c: #a28bc8;
  --header: rgba(13,16,19,.94);
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; background: var(--bg); }
body {
  margin: 0; color: var(--ink); background: var(--bg);
  font-family: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 15px; font-weight: 500; line-height: 1.45; -webkit-font-smoothing: antialiased;
}
a { color: inherit; text-underline-offset: 4px; }
button, input { font: inherit; }
.tutorial-header {
  position: sticky; top: 0; z-index: 20; display: flex; align-items: center;
  justify-content: space-between; min-height: 52px;
  padding: 0 max(24px, calc((100vw - var(--max)) / 2));
  border-bottom: 1px solid var(--line); background: var(--header); backdrop-filter: blur(12px);
}
.wordmark { font-weight: 750; letter-spacing: -.03em; text-decoration: none; }
.wordmark span { color: var(--accent); }
.tutorial-header nav { display: flex; align-items: center; gap: 20px; }
.tutorial-header nav a, .tutorial-header nav button { border: 0; padding: 0; color: var(--muted); background: none; font-size: .78rem; text-decoration: none; cursor: pointer; }
.tutorial-header nav a:hover, .tutorial-header nav button:hover { color: var(--ink); }
main, footer { width: min(calc(100% - 48px), var(--max)); margin-inline: auto; }
.tutorial-hero { max-width: 850px; margin: 0 auto; padding: 40px 0 26px; text-align: center; }
.eyebrow, .section-kicker {
  margin: 0 0 12px; color: var(--accent); font-size: .7rem; font-weight: 750;
  letter-spacing: .12em; text-transform: uppercase;
}
.tutorial-hero h1 {
  max-width: 760px; margin: 0 auto; font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(1.65rem, 7.5vw, 3rem); font-weight: 600; line-height: 1.04; letter-spacing: -.04em;
}
.tutorial-hero h1 > span { display: block; white-space: nowrap; }
.dek { max-width: 720px; margin: 16px auto 0; color: var(--muted); font-size: 1rem; line-height: 1.5; }
.paper-title { display: block; margin-top: 5px; color: var(--ink); font-family: Georgia, "Times New Roman", serif; font-size: 1.05em; font-style: normal; font-weight: 700; line-height: 1.4; }
.paper-byline { display: block; margin-top: 3px; }
.hero-author { color: var(--ink); font-weight: 650; text-decoration-thickness: 1px; }
.dek-follow { display: block; margin-top: 8px; }
.hero-actions { display: flex; justify-content: center; flex-wrap: wrap; gap: 8px; margin-top: 17px; }
.button {
  display: inline-flex; align-items: center; justify-content: center; min-height: 36px; padding: 0 14px;
  border: 1px solid var(--ink); border-radius: 20px; color: var(--ink); font-size: .8rem;
  font-weight: 700; text-decoration: none;
}
.button:hover { background: var(--surface); }
.button.quiet { border-color: var(--line-strong); font-weight: 600; }
.pec-core { margin: 4px 0 28px; padding: 18px; border: 1px solid var(--line); }
.pec-core-heading { display: grid; grid-template-columns: 1fr minmax(260px, 430px); gap: 28px; align-items: end; margin-bottom: 18px; }
.pec-core-heading .section-kicker { display: block; margin-bottom: 7px; }
.pec-core-heading h2 { margin: 0; font-family: Georgia, "Times New Roman", serif; font-size: clamp(1.7rem, 3vw, 2.45rem); font-weight: 600; line-height: 1.04; letter-spacing: -.035em; }
.pec-core-heading > p { margin: 0; color: var(--muted); font-size: .76rem; line-height: 1.45; }
.trace-system { position: relative; display: grid; grid-template-columns: 1fr 42px 1fr 42px 1fr 42px 1fr; align-items: stretch; padding: 5px 5px 11px; }
.trace-system::before { content: ""; position: absolute; z-index: -2; left: 12px; right: 12px; top: 50%; height: 1px; background: var(--line); }
.trace-stack { position: relative; isolation: isolate; min-width: 0; padding: 12px; border: 1px solid var(--line-strong); background: var(--bg); transition: transform .2s ease, border-color .2s ease, box-shadow .2s ease, background .2s ease; }
.trace-stack::before, .trace-stack::after { content: ""; position: absolute; z-index: -1; inset: 0; border: 1px solid var(--line); background: var(--surface); }
.trace-stack::before { transform: translate(3px,3px); }
.trace-stack::after { transform: translate(6px,6px); }
.core-p { --layer-color: var(--p); } .core-e { --layer-color: var(--e); }
.core-s { --layer-color: var(--s); } .core-c { --layer-color: var(--c); }
.trace-stack.is-related { transform: translateY(-3px); border-color: var(--ink); background: linear-gradient(180deg, var(--surface) 0 48px, var(--bg) 48px); box-shadow: inset 0 -3px var(--ink); }
.stack-title { display: flex; align-items: center; gap: 8px; padding-bottom: 9px; border-bottom: 1px solid var(--line); }
.stack-title b { display: grid; place-items: center; width: 29px; height: 29px; border: 1px solid currentColor; border-radius: 50%; background: var(--bg); font-family: Georgia, serif; font-size: 1rem; font-weight: 500; transition: background .2s ease, color .2s ease; }
.stack-title span { font-size: .69rem; font-weight: 750; letter-spacing: .05em; text-transform: uppercase; }
.core-p .stack-title b { color: var(--p); } .core-e .stack-title b { color: var(--e); }
.core-s .stack-title b { color: var(--s); } .core-c .stack-title b { color: var(--c); }
.trace-stack.is-related .stack-title b { border-color: var(--layer-color); background: var(--layer-color); color: var(--bg); }
.stack-chips { display: flex; flex-wrap: wrap; gap: 5px; margin-top: 11px; }
.stack-chips span { padding: 3px 7px; border: 1px solid var(--line); border-radius: 999px; background: var(--surface); color: var(--ink); font: 600 .58rem/1.2 ui-monospace, SFMono-Regular, Menlo, monospace; white-space: nowrap; }
.trace-stack.is-related .stack-chips span { border-color: var(--line-strong); background: var(--bg); }
.trace-stack p { margin: 11px 0 0; color: var(--muted); font-size: .65rem; }
.system-gap { position: relative; display: grid; place-items: center; }
.system-gap i { position: absolute; left: 5px; right: 5px; height: 1px; background: var(--line-strong); }
.system-gap b { z-index: 1; display: grid; place-items: center; width: 23px; height: 23px; border: 1px solid var(--line-strong); border-radius: 50%; background: var(--bg); font-family: Georgia, serif; font-size: .85rem; font-weight: 500; }
.core-audit-tabs { display: grid; grid-template-columns: repeat(4,1fr); margin-top: 7px; border: 1px solid var(--line); }
.core-audit-tabs button { position: relative; padding: 10px 12px; border: 0; border-right: 1px solid var(--line); background: var(--bg); color: var(--muted); text-align: left; cursor: pointer; }
.core-audit-tabs button:last-child { border-right: 0; }
.core-audit-tabs button::after { content: ""; position: absolute; right: 10px; top: 14px; width: 0; height: 0; border-top: 4px solid transparent; border-bottom: 4px solid transparent; border-left: 6px solid var(--line-strong); transition: transform .18s ease; }
.core-audit-tabs button:hover::after, .core-audit-tabs button:focus-visible::after { transform: translateX(2px); border-left-color: var(--ink); }
.core-audit-tabs button.active { background: var(--ink); color: var(--bg); }
.core-audit-tabs button.active::after { border-left-color: var(--bg); transform: rotate(90deg); }
.core-audit-tabs span, .core-audit-tabs b, .core-audit-tabs small { display: block; }
.core-audit-tabs span { font-family: Georgia, serif; font-size: .74rem; }
.core-audit-tabs b { margin-top: 3px; color: inherit; font-size: .69rem; }
.core-audit-tabs small { margin-top: 2px; color: inherit; font-size: .58rem; opacity: .72; }
.core-lens { display: grid; grid-template-columns: 1.35fr 1fr; border: 1px solid var(--line); border-top: 0; background: var(--bg); }
.core-lens-question { display: grid; grid-template-columns: 54px 1fr; gap: 12px; align-items: start; padding: 14px 16px; border-right: 1px solid var(--line); }
.core-lens-question > span { padding-top: 2px; font-family: Georgia, serif; font-size: 1.05rem; }
.core-lens h3 { margin: 0; font-family: Georgia, serif; font-size: 1.15rem; font-weight: 600; }
.core-lens-question p { margin: 5px 0 0; color: var(--muted); font-size: .69rem; }
.core-lens-toolbox { min-width: 0; }
.core-lens-methods { display: flex; align-content: center; flex-wrap: wrap; gap: 5px; padding: 12px 14px 10px; }
.core-lens-methods button { padding: 5px 7px; border: 1px solid var(--line-strong); background: var(--bg); color: var(--ink); font: 600 .62rem/1.2 ui-monospace, SFMono-Regular, Menlo, monospace; cursor: pointer; transition: background .16s ease, color .16s ease, transform .16s ease; }
.core-lens-methods button:hover, .core-lens-methods button:focus-visible { transform: translateY(-1px); border-color: var(--ink); }
.core-lens-methods button.active { background: var(--ink); color: var(--bg); }
.core-method-note { display: grid; grid-template-columns: 100px 1fr; gap: 9px; min-height: 46px; margin: 0; padding: 9px 14px; border-top: 1px solid var(--line); font-size: .64rem; }
.core-method-note b { font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }
.core-method-note span { color: var(--muted); }
.core-lens-boundary { grid-column: 1 / -1; display: grid; grid-template-columns: 135px 1fr; gap: 12px; margin: 0; padding: 9px 16px 9px 13px; border-top: 1px solid var(--line); border-left: 3px solid var(--accent); background: var(--bg); font-size: .67rem; }
.core-lens-boundary b { text-transform: uppercase; letter-spacing: .06em; }
.core-lens-boundary span { color: var(--muted); }
.progress-nav { display: grid; grid-template-columns: repeat(5,1fr); border-block: 1px solid var(--line); }
.progress-nav a { display: flex; align-items: center; gap: 9px; padding: 8px 11px; border-right: 1px solid var(--line); text-decoration: none; }
.progress-nav a:last-child { border-right: 0; }
.progress-nav b { font-family: Georgia, serif; font-size: 1.2rem; font-weight: 400; }
.progress-nav span { color: var(--muted); font-size: .72rem; }
.tutorial-section { padding: 32px 0; scroll-margin-top: 52px; }
.section-heading { display: grid; grid-template-columns: 1fr auto; align-items: end; gap: 24px; margin-bottom: 18px; }
.section-heading h2, .closing-section h2 {
  max-width: 850px; margin: 0; font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(1.6rem, 2.45vw, 2.12rem); font-weight: 600; line-height: 1.08; letter-spacing: -.03em;
}
.section-heading p { max-width: 780px; margin: 7px 0 0; color: var(--muted); }
.scenario-tabs { display: flex; gap: 5px; padding: 4px; border: 1px solid var(--line); background: var(--surface); }
.scenario-tabs button, .reset-button {
  border: 0; padding: 7px 10px; background: transparent; color: var(--muted); font-size: .72rem; cursor: pointer;
}
.scenario-tabs button.active { background: var(--ink); color: var(--bg); }
.journey-grid { position: relative; display: grid; grid-template-columns: repeat(4,1fr); gap: 12px; }
.journey-grid::before {
  content: ""; position: absolute; top: 35px; left: 11%; right: 11%; height: 1px; background: var(--line-strong); z-index: -1;
}
.trace-card { min-height: 120px; padding: 11px 12px; border: 1px solid var(--line); background: var(--bg); }
.trace-card > span {
  display: grid; place-items: center; width: 32px; height: 32px; border: 1px solid currentColor;
  border-radius: 50%; background: var(--bg); font-family: Georgia, serif; font-size: 1.2rem;
}
.p-card > span { color: var(--p); } .e-card > span { color: var(--e); }
.s-card > span { color: var(--s); } .c-card > span { color: var(--c); }
.trace-card small { display: block; margin-top: 12px; color: var(--muted); font-size: .66rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; }
.trace-card h3 { margin: 5px 0 4px; font-family: Georgia, serif; font-size: 1.25rem; font-weight: 500; }
.trace-card p { margin: 0; color: var(--muted); font-size: .78rem; }
.interpretation-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 12px; }
.interpretation-grid > div { padding: 15px 17px; background: var(--surface); }
.interpretation-grid span, .output-label { color: var(--accent); font-size: .63rem; font-weight: 750; letter-spacing: .09em; text-transform: uppercase; }
.interpretation-grid p { margin: 7px 0 0; font-size: .82rem; }
.preference-lab { display: grid; grid-template-columns: .85fr 1.15fr; margin-top: 20px; border: 1px solid var(--line); }
.preference-intro { padding: 15px 16px; border-right: 1px solid var(--line); background: var(--surface); }
.mini-kicker { color: var(--p); font-size: .63rem; font-weight: 750; letter-spacing: .09em; text-transform: uppercase; }
.preference-intro h3 { margin: 9px 0; font-family: Georgia, serif; font-size: 1.5rem; font-weight: 500; line-height: 1.15; }
.preference-intro p { margin: 9px 0 0; color: var(--muted); font-size: .78rem; }
.preference-controls { padding: 11px 15px; }
.preference-head, .preference-row { display: grid; grid-template-columns: 92px 1fr 28px 1fr 28px; gap: 8px; align-items: center; }
.preference-head { min-height: 30px; color: var(--muted); font-size: .61rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; }
.preference-head span:nth-child(2) { grid-column: 2 / 4; } .preference-head span:nth-child(3) { grid-column: 4 / 6; }
.preference-row { min-height: 39px; border-top: 1px solid var(--line); }
.preference-row b { font-size: .72rem; } .preference-row output { color: var(--muted); font-family: ui-monospace, monospace; font-size: .68rem; }
.preference-output { grid-column: 1 / -1; display: grid; grid-template-columns: repeat(3,1fr); border-top: 1px solid var(--line); }
.preference-output > div { padding: 10px 14px; border-right: 1px solid var(--line); }
.preference-output > div:last-child { border-right: 0; }
.preference-output span, .preference-output small { display: block; color: var(--muted); font-size: .61rem; }
.preference-output span { min-height: 20px; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; }
.preference-output strong { display: block; font-family: Georgia, serif; font-size: 1.35rem; font-weight: 500; }
.formula-disclosure { grid-column: 1 / -1; border-top: 1px solid var(--line); background: var(--surface); }
.formula-disclosure summary { padding: 11px 16px; color: var(--ink); font-size: .72rem; font-weight: 700; cursor: pointer; list-style-position: inside; }
.formula-disclosure[open] summary { border-bottom: 1px solid var(--line); }
.formula-grid { display: grid; grid-template-columns: repeat(3,1fr); }
.formula-grid.four { grid-template-columns: repeat(4,1fr); }
.formula-grid > div { min-width: 0; padding: 14px 16px; border-right: 1px solid var(--line); }
.formula-grid > div:last-child { border-right: 0; }
.formula-grid b { display: block; margin-bottom: 7px; font-size: .7rem; }
.formula-grid code { display: block; color: var(--ink); font-family: Georgia, "Times New Roman", serif; font-size: .88rem; line-height: 1.35; overflow-wrap: anywhere; white-space: normal; }
.formula-grid p { margin: 8px 0 0; color: var(--muted); font-size: .69rem; }
.formula-note { margin: 0; padding: 10px 16px; border-top: 1px solid var(--line); color: var(--muted); font-size: .68rem; }
.trace-lab { display: grid; grid-template-columns: 1.06fr .94fr; border: 1px solid var(--line); }
.trace-input { padding: 14px 16px 16px; }
.trace-input-head { display: flex; justify-content: space-between; gap: 16px; padding-bottom: 9px; border-bottom: 1px solid var(--line); font-size: .66rem; }
.trace-input-head b { letter-spacing: .08em; text-transform: uppercase; }
.trace-input-head span { color: var(--muted); }
.click-table { display: grid; grid-template-columns: 1fr 1fr; }
.click-item { display: grid; grid-template-columns: 20px 1fr; gap: 8px; align-items: center; min-height: 49px; padding: 6px 8px 6px 0; border-bottom: 1px solid var(--line); cursor: pointer; }
.click-item:nth-child(odd) { border-right: 1px solid var(--line); }
.click-item:nth-child(even) { padding-left: 12px; }
.click-item input { width: 15px; height: 15px; margin: 0; accent-color: var(--accent); }
.click-item b, .click-item small { display: block; }
.click-item b { font-size: .75rem; font-weight: 650; }
.click-item small { margin-top: 2px; color: var(--muted); font-size: .64rem; }
.trace-output { padding: 16px 18px; border-left: 1px solid var(--line); background: var(--surface); }
.trace-equation { display: flex; align-items: center; gap: 5px; margin: 10px 0 9px; font-family: Georgia, "Times New Roman", serif; font-size: 1.05rem; }
.trace-equation > strong { margin-left: 3px; font-size: 1.85rem; font-weight: 500; }
.fraction { display: inline-grid; grid-template-rows: 1fr 1fr; min-width: 28px; text-align: center; line-height: 1.05; }
.fraction b { font-weight: 500; }
.fraction b:first-child { padding-bottom: 2px; border-bottom: 1px solid currentColor; }
.fraction b:last-child { padding-top: 2px; }
.trace-composition { height: 7px; overflow: hidden; background: var(--line); }
.trace-composition i { display: block; width: 25%; height: 100%; background: var(--accent); transition: width .2s ease; }
.trace-output > p { margin: 10px 0; color: var(--muted); font-size: .75rem; }
.trace-output p b { color: var(--ink); }
.trace-boundary { display: grid; grid-template-columns: 1fr 1fr; border-top: 1px solid var(--line); }
.trace-boundary > div { padding: 9px 10px 0 0; }
.trace-boundary > div + div { padding-left: 10px; border-left: 1px solid var(--line); }
.trace-boundary b, .trace-boundary span { display: block; }
.trace-boundary b { margin-bottom: 4px; font-size: .65rem; text-transform: uppercase; letter-spacing: .06em; }
.trace-boundary span { color: var(--muted); font-size: .66rem; line-height: 1.4; }
.trace-paper { grid-column: 1 / -1; display: grid; grid-template-columns: 1.7fr repeat(4,.72fr); border-top: 1px solid var(--line); }
.trace-paper-copy, .trace-paper-metric { padding: 12px 14px; border-right: 1px solid var(--line); }
.trace-paper-copy p { margin: 6px 0 0; color: var(--muted); font-size: .7rem; line-height: 1.45; }
.trace-paper-metric span, .trace-paper-metric small { display: block; color: var(--muted); font-size: .61rem; }
.trace-paper-metric span { text-transform: uppercase; letter-spacing: .06em; }
.trace-paper-metric strong { display: block; margin: 3px 0 1px; font-family: Georgia, serif; font-size: 1.35rem; font-weight: 500; white-space: nowrap; }
.trace-paper-metric strong em { font-family: inherit; font-size: .64rem; font-style: normal; }
.trace-paper-metric small i { display: inline-block; width: 10px; height: 3px; margin-right: 4px; background: var(--ink); vertical-align: middle; }
.trace-paper-metric small i.baseline { background: var(--line-strong); }
.trace-paper-lesson { grid-column: 1 / -1; margin: 0; padding: 9px 14px; border-top: 1px solid var(--line); color: var(--muted); font-size: .7rem; }
.trace-paper-lesson b { color: var(--ink); }
.small { color: var(--muted); font-size: .72rem !important; font-weight: 500; }
.reset-button { border: 1px solid var(--line-strong); }
.reset-button:hover { color: var(--ink); background: var(--surface); }
.metric-lab { display: grid; grid-template-columns: 1.12fr .88fr; gap: 14px; }
.slider-panel, .distribution-panel { border: 1px solid var(--line); padding: 14px; }
.slider-head, .slider-row { display: grid; grid-template-columns: 110px 1fr 32px 1fr 32px; gap: 9px; align-items: center; }
.slider-head { margin-bottom: 7px; color: var(--muted); font-size: .62rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; }
.slider-head span:nth-child(2) { grid-column: 2 / 4; } .slider-head span:nth-child(3) { grid-column: 4 / 6; }
.slider-row { min-height: 42px; border-top: 1px solid var(--line); }
.slider-row b { font-size: .76rem; font-weight: 600; }
.slider-row output { color: var(--muted); font-family: ui-monospace, monospace; font-size: .7rem; }
input[type="range"] { width: 100%; accent-color: var(--accent); }
.distribution-panel { display: block; }
.chart-heading { display: flex; justify-content: space-between; align-items: center; color: var(--muted); font-size: .62rem; font-weight: 700; letter-spacing: .07em; text-transform: uppercase; }
.chart-heading div { display: flex; align-items: center; gap: 6px; letter-spacing: 0; text-transform: none; }
.chart-heading i { width: 14px; height: 3px; margin-left: 6px; background: var(--e); }
.chart-heading i.legend-clicks { background: var(--c); }
.distribution-chart { display: block; width: 100%; height: auto; margin-top: 8px; overflow: visible; }
.chart-grid line { stroke: var(--line); stroke-width: 1; } .chart-grid text { fill: var(--muted); font-size: 9px; }
.chart-grid text.category-label { font-size: 9px; text-anchor: middle; }
.distribution-area { opacity: .13; } .exposure-area { fill: var(--e); } .click-area { fill: var(--c); }
.distribution-line { fill: none; stroke-width: 2.2; stroke-linejoin: round; stroke-linecap: round; transition: points .2s ease; }
.exposure-line { stroke: var(--e); } .click-line { stroke: var(--c); }
.distribution-point { stroke: var(--bg); stroke-width: 2; } .distribution-point.exposure { fill: var(--e); } .distribution-point.clicks { fill: var(--c); }
.entropy-visual { margin-top: 4px; padding-top: 11px; border-top: 1px solid var(--line); }
.entropy-scale { display: grid; grid-template-columns: 1fr auto 1fr; align-items: center; margin-bottom: 8px; color: var(--muted); font-size: .56rem; }
.entropy-scale b { color: var(--ink); font-size: .61rem; text-align: center; text-transform: uppercase; letter-spacing: .06em; }
.entropy-scale span:last-child { text-align: right; }
.entropy-row { display: grid; grid-template-columns: 58px 1fr 166px; gap: 8px; align-items: center; margin: 7px 0; }
.entropy-row > b { font-size: .65rem; }
.entropy-row > strong { color: var(--muted); font-size: .61rem; font-weight: 600; text-align: right; }
.entropy-track { height: 8px; overflow: hidden; background: var(--surface); }
.entropy-track i { display: block; height: 100%; background: var(--e); transition: width .2s ease; }
.entropy-row:last-child .entropy-track i { background: var(--c); }
.metric-output { display: grid; grid-template-columns: repeat(4,1fr); margin-top: 16px; border-block: 1px solid var(--line); }
.metric-output > div { padding: 12px 14px; border-right: 1px solid var(--line); }
.metric-output > div:last-child { border-right: 0; }
.metric-output span { display: block; min-height: 28px; color: var(--muted); font-size: .66rem; font-weight: 700; text-transform: uppercase; }
.metric-output strong { font-family: Georgia, serif; font-size: 1.65rem; font-weight: 400; }
.metric-reading { margin: 10px 0 0; color: var(--muted); font-size: .78rem; }
.concept-strip { display: grid; grid-template-columns: repeat(3,1fr); margin-top: 10px; border: 1px solid var(--line); }
.concept-strip span { padding: 9px 12px; border-right: 1px solid var(--line); color: var(--muted); font-size: .67rem; }
.concept-strip span:last-child { border-right: 0; }
.concept-strip b { display: block; color: var(--ink); font-size: .7rem; }
.metric-formulas { margin-top: 12px; border: 1px solid var(--line); }
.evidence-tabs { display: grid; grid-template-columns: repeat(4,1fr); border: 1px solid var(--line); }
.evidence-tabs button { padding: 12px 14px; border: 0; border-right: 1px solid var(--line); background: var(--bg); color: var(--muted); font-size: .72rem; text-align: left; cursor: pointer; }
.evidence-tabs button:last-child { border-right: 0; }
.evidence-tabs button b { display: block; margin-bottom: 2px; color: var(--ink); }
.evidence-tabs button.active { background: var(--ink); color: var(--bg); }
.evidence-tabs button.active b { color: inherit; }
.evidence-panel { min-height: 0; padding: 18px; border: 1px solid var(--line); border-top: 0; }
.evidence-lead { display: grid; grid-template-columns: 1fr 190px; gap: 22px; align-items: start; }
.evidence-lead h3 { max-width: 700px; margin: 0; font-family: Georgia, serif; font-size: 1.65rem; font-weight: 500; line-height: 1.18; }
.evidence-lead p { max-width: 720px; margin: 9px 0 0; color: var(--muted); font-size: .8rem; }
.evidence-sample { padding: 10px 12px; border-left: 2px solid var(--accent); background: var(--surface); color: var(--muted); font-size: .68rem; }
.evidence-sample b { display: block; color: var(--ink); font-size: .82rem; }
.evidence-controls { display: flex; flex-wrap: wrap; gap: 5px; margin-top: 14px; }
.evidence-controls button { padding: 6px 9px; border: 1px solid var(--line); background: var(--bg); color: var(--muted); font-size: .67rem; cursor: pointer; }
.evidence-controls button.active { border-color: var(--ink); background: var(--ink); color: var(--bg); }
.evidence-visuals { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-top: 16px; }
.evidence-chart { padding: 14px; border: 1px solid var(--line); }
.evidence-chart > span { display: block; margin-bottom: 14px; color: var(--muted); font-size: .62rem; font-weight: 700; letter-spacing: .07em; text-transform: uppercase; }
.result-row { display: grid; grid-template-columns: 130px 1fr 48px; align-items: center; gap: 10px; margin: 10px 0; font-size: .72rem; }
.result-track { height: 14px; background: var(--surface); }
.result-track i { display: block; height: 100%; background: var(--ink); transition: width .25s ease; }
.result-row em { color: var(--muted); font-style: normal; text-align: right; }
.stacked-result { display: flex; height: 30px; overflow: hidden; background: var(--surface); }
.stacked-result i { display: grid; place-items: center; min-width: 52px; height: 100%; color: #fff; font-size: .65rem; font-style: normal; }
.stacked-result i:first-child { background: var(--p); } .stacked-result i:last-child { background: var(--line-strong); }
.metric-definition { margin: 13px 0 0; color: var(--muted); font-size: .69rem; }
.metric-definition b { color: var(--ink); }
.evidence-takeaway { margin-top: 12px; padding: 10px 13px; border-left: 3px solid var(--accent); background: var(--surface); font-size: .78rem; }
.evidence-takeaway b { display: block; margin-bottom: 3px; }
.dot-scale { position: relative; height: 72px; margin: 12px 12px 0; border-bottom: 1px solid var(--line-strong); }
.dot-scale::before, .dot-scale::after { position: absolute; bottom: -20px; color: var(--muted); font-size: .62rem; }
.dot-scale::before { content: "0%"; left: 0; } .dot-scale::after { content: "18%"; right: 0; }
.dot-scale.auc::before { content: "0.50"; } .dot-scale.auc::after { content: "0.90"; }
.ci-line { position: absolute; top: 31px; height: 2px; background: var(--line-strong); }
.chart-dot { position: absolute; top: 24px; width: 15px; height: 15px; border: 3px solid var(--bg); border-radius: 50%; background: var(--e); box-shadow: 0 0 0 1px var(--e); transform: translateX(-50%); }
.chart-dot.baseline { top: 48px; width: 10px; height: 10px; border: 0; background: var(--line-strong); box-shadow: none; }
.dot-label { position: absolute; top: 0; color: var(--muted); font-size: .62rem; transform: translateX(-50%); white-space: nowrap; }
.claim-lab { display: grid; grid-template-columns: .9fr 1.1fr; border: 1px solid var(--line); }
.claim-list { display: grid; border-right: 1px solid var(--line); }
.claim-list button { display: grid; grid-template-columns: 1fr 18px; align-items: center; gap: 8px; padding: 9px 13px; border: 0; border-bottom: 1px solid var(--line); background: var(--bg); color: var(--muted); text-align: left; cursor: pointer; }
.claim-list button::after { content: "→"; color: var(--line-strong); font-size: .82rem; text-align: right; transition: transform .18s ease, color .18s ease; }
.claim-list button:last-child { border-bottom: 0; }
.claim-list button:hover, .claim-list button.active { color: var(--ink); background: var(--surface); }
.claim-list button:hover::after { color: var(--ink); transform: translateX(2px); }
.claim-list button.active { box-shadow: inset 3px 0 var(--accent); }
.claim-list button.active::after { content: "▶"; color: var(--ink); font-size: .6rem; transform: none; }
.claim-result { min-height: 270px; padding: 18px 20px; background: var(--surface); }
.claim-result-head { display: flex; align-items: center; justify-content: space-between; gap: 14px; }
.status { display: inline-block; padding: 4px 8px; border: 1px solid currentColor; color: var(--p); font-size: .7rem; font-weight: 750; letter-spacing: .08em; text-transform: uppercase; }
.status.bounded { color: var(--s); } .status.unsupported { color: var(--c); }
.claim-result h3 { margin: 14px 0 8px; font-family: Georgia, serif; font-size: 1.65rem; font-weight: 500; line-height: 1.14; }
.claim-result > p { max-width: 650px; margin: 0; color: var(--muted); font-size: .9rem; line-height: 1.5; }
.evidence-chips { display: flex; gap: 5px; }
.evidence-chips b { display: grid; place-items: center; width: 31px; height: 31px; border: 1px solid var(--line-strong); border-radius: 50%; font-family: Georgia, serif; font-weight: 400; }
.evidence-chips .evidence-p { border-color: var(--p); color: var(--p); }
.evidence-chips .evidence-e { border-color: var(--e); color: var(--e); }
.evidence-chips .evidence-s { border-color: var(--s); color: var(--s); }
.evidence-chips .evidence-c { border-color: var(--c); color: var(--c); }
.evidence-chips .evidence-unknown { border-style: dashed; color: var(--muted); }
.claim-reasoning { display: grid; grid-template-columns: 1fr 1fr; margin-top: 14px; border-block: 1px solid var(--line); }
.claim-reasoning > div { padding: 10px 12px 10px 0; }
.claim-reasoning > div + div { padding-left: 12px; border-left: 1px solid var(--line); }
.claim-reasoning span { display: block; margin-bottom: 6px; color: var(--ink); font-size: .7rem; font-weight: 750; letter-spacing: .07em; text-transform: uppercase; }
.claim-reasoning p { margin: 0; color: var(--muted); font-size: .82rem; line-height: 1.48; }
.claim-result .claim-rewrite { display: grid; grid-template-columns: 104px 1fr; gap: 12px; align-items: start; margin-top: 13px; color: var(--ink); }
.claim-rewrite b { font-size: .72rem; line-height: 1.35; text-transform: uppercase; letter-spacing: .05em; }
.claim-rewrite span { color: var(--muted); font-size: .84rem; line-height: 1.45; }
.lessons-section { padding: 32px 0 14px; }
.lessons-section > h2 { max-width: 780px; margin: 0 0 20px; font-family: Georgia, "Times New Roman", serif; font-size: clamp(1.85rem, 3.4vw, 2.7rem); font-weight: 600; line-height: 1.08; letter-spacing: -.035em; }
.lesson-grid { display: grid; grid-template-columns: 1fr 1fr; border: 1px solid var(--line); }
.lesson-grid article { min-height: 108px; padding: 12px 15px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.lesson-grid article:nth-child(2n) { border-right: 0; } .lesson-grid article:nth-last-child(-n+2) { border-bottom: 0; }
.lesson-grid b { color: var(--accent); font-family: Georgia, serif; font-size: .86rem; font-weight: 500; }
.lesson-grid h3 { margin: 7px 0 5px; font-family: Georgia, serif; font-size: 1.12rem; font-weight: 600; }
.lesson-grid p { margin: 0; color: var(--muted); font-size: .76rem; }
.lesson-thesis { margin: 0; padding: 14px 18px; border: 1px solid var(--line); border-top: 0; background: var(--surface); font-size: .79rem; }
.closing-section { max-width: 820px; margin: 12px auto 30px; padding: 22px; background: var(--surface); text-align: center; }
.closing-section h2 { margin-inline: auto; }
.closing-section p { max-width: 700px; margin: 16px auto 0; color: var(--muted); }
.closing-section .discussion-note { margin-top: 18px; padding-top: 15px; border-top: 1px solid var(--line); font-size: .76rem; }
.discussion-note a { color: var(--ink); font-weight: 700; text-decoration: underline; text-underline-offset: 3px; }
footer { display: flex; justify-content: space-between; padding: 20px 0 30px; border-top: 1px solid var(--line); color: var(--muted); font-size: .7rem; }
@media (max-width: 820px) {
  .tutorial-header nav { gap: 13px; } .tutorial-header nav a:nth-child(-n+3) { display: none; }
  main, footer { width: min(calc(100% - 32px), var(--max)); }
  .progress-nav { grid-template-columns: 1fr 1fr; }
  .pec-core-heading { grid-template-columns: 1fr; gap: 8px; }
  .trace-system { grid-template-columns: 1fr 28px 1fr; row-gap: 15px; }
  .trace-system .core-s { grid-column: 1; }
  .trace-system .core-c { grid-column: 3; }
  .trace-system .system-gap:nth-of-type(2) { display: none; }
  .core-audit-tabs { grid-template-columns: 1fr 1fr; }
  .core-audit-tabs button:nth-child(2) { border-right: 0; }
  .core-audit-tabs button:nth-child(-n+2) { border-bottom: 1px solid var(--line); }
  .core-lens { grid-template-columns: 1fr; }
  .core-lens-question { border-right: 0; border-bottom: 1px solid var(--line); }
  .progress-nav a:nth-child(2) { border-right: 0; } .progress-nav a:nth-child(-n+2) { border-bottom: 1px solid var(--line); }
  .section-heading, .trace-lab, .metric-lab, .claim-lab, .preference-lab { grid-template-columns: 1fr; }
  .journey-grid { grid-template-columns: 1fr 1fr; } .journey-grid::before { display: none; }
  .trace-output, .claim-list { border: 0; border-top: 1px solid var(--line); }
  .trace-paper { grid-template-columns: repeat(2,1fr); }
  .trace-paper-copy { grid-column: 1 / -1; border-right: 0; border-bottom: 1px solid var(--line); }
  .trace-paper-metric:nth-of-type(odd) { border-right: 0; }
  .claim-list { grid-template-columns: 1fr 1fr; }
  .claim-list button { border-right: 1px solid var(--line); }
  .claim-list button:nth-child(2n) { border-right: 0; }
  .claim-list button:last-child { grid-column: 1 / -1; border-right: 0; border-bottom: 0; }
  .preference-intro { border-right: 0; border-bottom: 1px solid var(--line); }
  .evidence-lead { grid-template-columns: 1fr; gap: 14px; }
  .metric-output { grid-template-columns: 1fr 1fr; }
  .metric-output > div:nth-child(2) { border-right: 0; }
  .metric-output > div:nth-child(-n+2) { border-bottom: 1px solid var(--line); }
}
@media (min-width: 641px) and (max-width: 820px) {
  .progress-nav { grid-template-columns: repeat(5,1fr); }
  .progress-nav a { border-right: 1px solid var(--line) !important; border-bottom: 0 !important; }
  .progress-nav a:last-child { border-right: 0 !important; }
  .journey-grid { grid-template-columns: repeat(4,1fr); }
  .preference-lab { grid-template-columns: .85fr 1.15fr; }
  .preference-intro { border-right: 1px solid var(--line); border-bottom: 0; }
  .trace-lab { grid-template-columns: 1.06fr .94fr; }
  .trace-output { border-top: 0; border-left: 1px solid var(--line); }
  .metric-lab { grid-template-columns: 1.05fr .95fr; }
  .claim-lab { grid-template-columns: .9fr 1.1fr; }
  .claim-list { grid-template-columns: 1fr; border-top: 0; border-right: 1px solid var(--line); }
  .claim-list button { grid-column: auto !important; border-right: 0; }
  .evidence-lead { grid-template-columns: 1fr 170px; }
}
@media (max-width: 540px) {
  body { font-size: 14px; }
  .tutorial-header nav a { display: none !important; }
  .tutorial-hero { padding-top: 34px; }
  .tutorial-section { padding: 30px 0; }
  .pec-core { padding: 14px; }
  .trace-system { grid-template-columns: 1fr; gap: 8px; padding-inline: 2px; }
  .trace-system::before { display: none; }
  .trace-system .trace-stack, .trace-system .core-s, .trace-system .core-c { grid-column: 1; }
  .system-gap { min-height: 28px; transform: none; }
  .system-gap i { inset: 0 auto 0 50%; width: 1px; height: auto; }
  .trace-system .system-gap:nth-of-type(2) { display: grid; }
  .core-audit-tabs { grid-template-columns: 1fr; }
  .core-audit-tabs button { border-right: 0; border-bottom: 1px solid var(--line); }
  .core-audit-tabs button:last-child { border-bottom: 0; }
  .core-lens-question { grid-template-columns: 1fr; gap: 5px; }
  .core-lens-boundary { grid-template-columns: 1fr; gap: 4px; }
  .journey-grid, .interpretation-grid { grid-template-columns: 1fr; }
  .preference-output, .evidence-tabs, .evidence-visuals { grid-template-columns: 1fr; }
  .concept-strip { grid-template-columns: 1fr; }
  .concept-strip span { border-right: 0; border-bottom: 1px solid var(--line); }
  .concept-strip span:last-child { border-bottom: 0; }
  .lesson-grid { grid-template-columns: 1fr; }
  .lesson-grid article { min-height: 0; border-right: 0; border-bottom: 1px solid var(--line) !important; }
  .lesson-grid article:last-child { border-bottom: 0 !important; }
  .formula-grid, .formula-grid.four { grid-template-columns: 1fr 1fr; }
  .formula-grid > div:nth-child(2n) { border-right: 0; }
  .preference-output > div { border-right: 0; border-bottom: 1px solid var(--line); }
  .preference-output > div:last-child { border-bottom: 0; }
  .evidence-tabs button { border-right: 0; border-bottom: 1px solid var(--line); }
  .evidence-tabs button:last-child { border-bottom: 0; }
  .evidence-panel { padding: 20px 16px; }
  .scenario-tabs { width: 100%; overflow-x: auto; }
  .claim-list { grid-template-columns: 1fr; }
  .claim-list button { grid-column: auto !important; border-right: 0; }
  .claim-reasoning { grid-template-columns: 1fr; }
  .claim-reasoning > div + div { padding-left: 0; border-top: 1px solid var(--line); border-left: 0; }
  .scenario-tabs button { white-space: nowrap; }
  .click-table, .trace-boundary, .trace-paper { grid-template-columns: 1fr; }
  .click-item:nth-child(odd) { border-right: 0; }
  .click-item:nth-child(even) { padding-left: 0; }
  .trace-paper-copy, .trace-paper-metric { grid-column: auto; border-right: 0; border-bottom: 1px solid var(--line); }
  .trace-paper-lesson { grid-column: auto; }
  .slider-head, .slider-row { grid-template-columns: 78px 1fr 26px 1fr 26px; gap: 5px; }
  .metric-output { grid-template-columns: 1fr; }
  .formula-grid, .formula-grid.four { grid-template-columns: 1fr; }
  .formula-grid > div { border-right: 0; border-bottom: 1px solid var(--line); }
  .formula-grid > div:last-child { border-bottom: 0; }
  .metric-output > div { border-right: 0; border-bottom: 1px solid var(--line); }
  .metric-output > div:last-child { border-bottom: 0; }
  .closing-section { padding: 28px 20px; }
}
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } .trace-stack, .core-lens-methods button, .trace-composition i, .bar-track i { transition: none; } }