:root {
  --cloud: #f4f7fb;
  --paper: #ffffff;
  --ink: #122132;
  --on-ink-muted: #a9c2da;
  --muted: #56687a;
  --line: #cad6e2;
  --line-strong: #8ea2b7;
  --indigo: #3156a6;
  --indigo-dark: #223f7e;
  --cyan: #257c93;
  --cyan-soft: #dceff3;
  --amber: #9f5d04;
  --amber-soft: #fff1d8;
  --crimson: #a83f50;
  --crimson-soft: #fbe5e9;
  --green: #237355;
  --green-soft: #e1f3eb;
  --shadow: 0 24px 70px rgb(25 52 81 / 10%);
  --display: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --body: "Avenir Next", Avenir, "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background:
    linear-gradient(90deg, transparent 49.9%, rgb(49 86 166 / 4%) 50%, transparent 50.1%) 50% 0 / min(92vw, 1180px) 100%,
    var(--cloud);
  font-family: var(--body);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a {
  color: inherit;
  text-decoration-thickness: 1px;
  text-underline-offset: 0.2em;
}

button,
input,
select {
  font: inherit;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

:focus-visible {
  outline: 3px solid #16749c;
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  z-index: 100;
  top: 0.75rem;
  left: 0.75rem;
  padding: 0.7rem 1rem;
  color: var(--paper);
  background: var(--ink);
  transform: translateY(-180%);
}

.skip-link:focus {
  transform: translateY(0);
}

.site-header {
  width: min(92vw, 1180px);
  min-height: 92px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 2rem;
  border-bottom: 1px solid var(--line);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.8rem;
  text-decoration: none;
}

.brand > span:last-child {
  display: grid;
  line-height: 1.2;
}

.brand strong {
  font-family: var(--display);
  font-size: 1.08rem;
  letter-spacing: -0.01em;
}

.brand small {
  margin-top: 0.18rem;
  color: var(--muted);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.brand-mark {
  width: 2.2rem;
  height: 2.2rem;
  display: flex;
  align-items: flex-end;
  gap: 3px;
  padding: 0.42rem;
  border: 1px solid var(--ink);
  border-radius: 50%;
}

.brand-mark i {
  flex: 1;
  display: block;
  border-radius: 999px;
  background: var(--indigo);
}

.brand-mark i:nth-child(1) { height: 42%; }
.brand-mark i:nth-child(2) { height: 78%; background: var(--cyan); }
.brand-mark i:nth-child(3) { height: 58%; background: var(--amber); }

.site-header nav {
  display: flex;
  align-items: center;
  gap: clamp(1rem, 3vw, 2.3rem);
}

.site-header nav a {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.07em;
  text-decoration: none;
  text-transform: uppercase;
}

.site-header nav a:hover {
  color: var(--indigo);
}

main,
footer {
  width: min(92vw, 1180px);
  margin-inline: auto;
}

.hero {
  min-height: 670px;
  display: grid;
  grid-template-columns: minmax(0, 1.38fr) minmax(320px, 0.72fr);
  gap: clamp(3rem, 8vw, 8rem);
  align-items: center;
  padding: 7rem 0 6rem;
}

.eyebrow {
  margin: 0 0 1rem;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.eyebrow span {
  margin-right: 0.65rem;
  color: var(--indigo-dark);
}

.hero h1,
.section-heading h2,
.neighbors h2 {
  font-family: var(--display);
  font-weight: 500;
  letter-spacing: -0.045em;
  line-height: 0.99;
}

.hero h1 {
  max-width: 800px;
  margin: 0;
  font-size: clamp(3.8rem, 7.2vw, 6.8rem);
}

.hero h1 em {
  color: var(--indigo);
  font-weight: 500;
}

.hero-lead {
  max-width: 670px;
  margin: 2rem 0 0;
  color: #42566a;
  font-size: clamp(1.1rem, 1.9vw, 1.35rem);
  line-height: 1.55;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-top: 2rem;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 0.75rem 1.1rem;
  border: 1px solid var(--indigo);
  border-radius: 4px;
  font-size: 0.82rem;
  font-weight: 750;
  letter-spacing: 0.04em;
  text-decoration: none;
}

.button.primary {
  color: white;
  background: var(--indigo);
}

.button.primary:hover { background: var(--indigo-dark); }
.button.quiet:hover { background: rgb(49 86 166 / 7%); }

.hero-proof {
  position: relative;
  padding: 2rem;
  border: 1px solid var(--line-strong);
  background: rgb(255 255 255 / 64%);
  box-shadow: 14px 14px 0 rgb(49 86 166 / 7%);
}

.hero-proof::before {
  position: absolute;
  top: -1px;
  left: -1px;
  width: 38%;
  height: 4px;
  content: "";
  background: linear-gradient(90deg, var(--indigo), var(--cyan));
}

.proof-label,
.metric-label,
.ledger-label,
.card-kicker {
  margin: 0;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.equation-stack {
  display: grid;
  gap: 0.45rem;
  padding: 2rem 0 1.6rem;
  font-family: var(--display);
  font-size: clamp(1.4rem, 3vw, 2rem);
  text-align: center;
}

.equation-stack strong {
  color: var(--indigo-dark);
  font-weight: 600;
}

.proof-rule {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 0.5rem;
  align-items: center;
  color: var(--cyan);
  font-family: var(--mono);
  font-size: 0.62rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.proof-rule span { height: 1px; background: var(--cyan); }
.hero-proof > p:last-child { margin: 1.4rem 0 0; color: var(--muted); font-size: 0.88rem; }

.route-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border: 1px solid var(--line);
  background: var(--paper);
  box-shadow: var(--shadow);
}

.route-grid a {
  min-height: 170px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  padding: 1.5rem;
  text-decoration: none;
}

.route-grid a + a { border-left: 1px solid var(--line); }
.route-grid a:hover { background: #f8faff; }
.route-grid a span { margin-bottom: auto; color: var(--indigo); font-family: var(--mono); font-size: 0.7rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; }
.route-grid a strong { font-family: var(--display); font-size: 1.2rem; }
.route-grid a small { margin-top: 0.35rem; color: var(--muted); font-size: 0.78rem; line-height: 1.45; }

.section {
  padding: clamp(6rem, 11vw, 10rem) 0;
}

.section-heading {
  max-width: 840px;
  margin-bottom: 4rem;
}

.section-heading.compact { margin-bottom: 2.5rem; }
.section-heading h2,
.neighbors h2 {
  margin: 0;
  font-size: clamp(2.7rem, 5.5vw, 5rem);
}

.section-heading > p:last-child {
  max-width: 730px;
  margin: 1.5rem 0 0;
  color: var(--muted);
  font-size: 1.05rem;
}

.concept-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  border-top: 1px solid var(--line-strong);
  border-bottom: 1px solid var(--line-strong);
}

.concept-grid article {
  display: grid;
  grid-template-rows: auto auto 1fr auto;
  padding: 2rem;
}

.concept-grid article + article { border-left: 1px solid var(--line); }
.concept-index { width: 2.3rem; height: 2.3rem; display: grid; place-items: center; margin: 0 0 2rem; border-radius: 50%; color: white; background: var(--indigo); font-family: var(--mono); font-size: 0.72rem; }
.concept-grid article:nth-child(2) .concept-index { background: var(--cyan); }
.concept-grid article:nth-child(3) .concept-index { background: var(--amber); }
.concept-grid h3 { margin: 0; font-family: var(--display); font-size: 1.45rem; }
.concept-grid p:not(.concept-index) { color: var(--muted); font-size: 0.9rem; }
.concept-grid code { display: block; overflow-x: auto; padding-top: 1.2rem; border-top: 1px solid var(--line); color: var(--ink); font-family: var(--mono); font-size: 0.76rem; white-space: nowrap; }

.precision-note {
  max-width: 850px;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  margin: 2rem 0 0 auto;
  padding: 1.2rem 1.5rem;
  color: #72500d;
  background: var(--amber-soft);
  border-left: 3px solid var(--amber);
  font-size: 0.86rem;
}

.precision-note > span { font-family: var(--mono); font-size: 1.4rem; }

.run {
  width: 100vw;
  margin-left: calc(50% - 50vw);
  padding-inline: max(4vw, calc((100vw - 1180px) / 2));
  background: #eaf0f7;
  border-block: 1px solid var(--line);
}

.lab-shell {
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  border: 1px solid var(--line-strong);
  background: var(--paper);
  box-shadow: var(--shadow);
}

.controls {
  padding: 1.6rem;
  background: #f8fafd;
  border-right: 1px solid var(--line);
}

.control-heading {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-bottom: 1.8rem;
}

.control-heading div { display: flex; align-items: center; gap: 0.5rem; font-size: 0.8rem; }
.group-dot { width: 0.7rem; height: 0.7rem; display: inline-block; border-radius: 50%; background: var(--indigo); }
.group-dot.b { background: var(--cyan); }

.controls fieldset {
  margin: 0 0 1.6rem;
  padding: 0;
  border: 0;
}

.controls legend,
.select-label {
  width: 100%;
  display: block;
  margin-bottom: 0.7rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.controls label:not(.select-label) {
  display: flex;
  justify-content: space-between;
  margin: 0.45rem 0 0.1rem;
  color: var(--muted);
  font-size: 0.73rem;
}

.controls output {
  color: var(--ink);
  font-family: var(--mono);
}

input[type="range"] {
  width: 100%;
  height: 24px;
  margin: 0;
  accent-color: var(--indigo);
}

input[id$="-b"] { accent-color: var(--cyan); }

select {
  width: 100%;
  min-height: 44px;
  padding: 0.55rem;
  color: var(--ink);
  border: 1px solid var(--line-strong);
  border-radius: 3px;
  background: white;
  font-size: 0.78rem;
}

.reset-button {
  width: 100%;
  min-height: 42px;
  margin-top: 1rem;
  color: var(--indigo-dark);
  border: 1px solid var(--line-strong);
  border-radius: 3px;
  background: transparent;
  cursor: pointer;
  font-size: 0.76rem;
  font-weight: 700;
}

.reset-button:hover { background: white; }
.lab-output { min-width: 0; padding: clamp(1.4rem, 3vw, 2.6rem); }

.sample-summary {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  align-items: stretch;
  border-bottom: 1px solid var(--line);
}

.sample-summary > div { display: grid; padding: 0 0 1.4rem; }
.sample-summary > div:nth-child(3) { text-align: right; }
.sample-summary .contrast { text-align: center; border-inline: 1px solid var(--line); }
.sample-summary span { color: var(--muted); font-family: var(--mono); font-size: 0.66rem; letter-spacing: 0.08em; text-transform: uppercase; }
.sample-summary strong { margin: 0.2rem 0; font-family: var(--display); font-size: 1.7rem; font-weight: 500; }
.sample-summary .contrast strong { color: var(--indigo); }
.sample-summary small { color: var(--muted); font-size: 0.7rem; }

figure { margin: 0; }
figure figcaption { display: flex; justify-content: space-between; gap: 1rem; margin: 1.5rem 0 0.6rem; }
figure figcaption strong { font-size: 0.8rem; }
figure figcaption span { color: var(--muted); font-size: 0.7rem; }
figure svg { width: 100%; height: auto; display: block; overflow: visible; }

.method-picker {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin: 1.5rem 0;
  border: 1px solid var(--line-strong);
}

.method-picker button {
  min-height: 56px;
  padding: 0.55rem;
  color: var(--muted);
  border: 0;
  background: white;
  cursor: pointer;
  font-size: 0.77rem;
  font-weight: 700;
}

.method-picker button + button { border-left: 1px solid var(--line); }
.method-picker button small { display: block; font-size: 0.58rem; font-weight: 500; }
.method-picker button[aria-pressed="true"] { color: white; background: var(--indigo); }

.selected-method {
  display: grid;
  grid-template-columns: 0.75fr 1.25fr;
  gap: 2rem;
  align-items: end;
  margin-top: 1.5rem;
  padding: 1.5rem;
  background: var(--ink);
  color: white;
}

.selected-method .metric-label { color: #a9c2da; }
.selected-method .metric { display: block; margin: 0.3rem 0 0; font-family: var(--display); font-size: 2.7rem; font-weight: 500; }
.selected-method > div > p:last-child { margin: 0; color: #c9d7e5; font-family: var(--mono); font-size: 0.68rem; }
.selected-method dl { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0.8rem; margin: 0; }
.selected-method dl div { padding-left: 0.8rem; border-left: 1px solid #4b6075; }
.selected-method dt { color: #9fb2c5; font-size: 0.63rem; }
.selected-method dd { margin: 0.2rem 0 0; font-family: var(--mono); font-size: 0.8rem; }

.method-ledger { padding: 1.5rem; border: 1px solid var(--line); border-top: 0; }
.method-ledger h3 { margin: 0.2rem 0 1rem; font-family: var(--display); font-size: 1.5rem; }
.method-ledger dl { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1rem 1.5rem; margin: 0; }
.method-ledger dl div { padding-top: 0.8rem; border-top: 1px solid var(--line); }
.method-ledger dt { color: var(--indigo-dark); font-family: var(--mono); font-size: 0.63rem; font-weight: 700; letter-spacing: 0.05em; text-transform: uppercase; }
.method-ledger dd { margin: 0.3rem 0 0; color: var(--muted); font-size: 0.76rem; }

.real-case {
  margin-top: 2rem;
  padding: clamp(1.6rem, 4vw, 3rem);
  border: 1px solid var(--line-strong);
  background: var(--paper);
  box-shadow: var(--shadow);
}

.real-case header { max-width: 860px; }
.real-case h3 { margin: 0; font-family: var(--display); font-size: clamp(1.8rem, 3.5vw, 3rem); font-weight: 500; line-height: 1.08; }
.real-case header > p:last-child { max-width: 760px; margin: 1rem 0 0; color: var(--muted); }
.case-metrics { display: grid; grid-template-columns: repeat(4, 1fr); margin-top: 2rem; border-block: 1px solid var(--line-strong); }
.case-metrics > div { min-width: 0; display: grid; align-content: start; padding: 1.4rem; }
.case-metrics > div + div { border-left: 1px solid var(--line); }
.case-metrics span { color: var(--muted); font-family: var(--mono); font-size: 0.65rem; font-weight: 700; letter-spacing: 0.05em; text-transform: uppercase; }
.case-metrics strong { margin: 0.35rem 0 0.1rem; font-family: var(--display); font-size: clamp(1.35rem, 2.5vw, 2rem); font-weight: 500; white-space: nowrap; }
.case-metrics small { color: var(--muted); font-size: 0.7rem; }
.case-metrics .case-contrast { background: var(--cyan-soft); }
.case-metrics .case-contrast strong { color: var(--indigo-dark); }
.case-boundary { display: grid; grid-template-columns: 1fr 1fr; gap: 1.5rem; margin-top: 1.5rem; }
.case-boundary p { margin: 0; color: var(--muted); font-size: 0.82rem; }
.case-boundary strong { color: var(--ink); }
.case-source { margin: 1.5rem 0 0; padding-top: 1rem; border-top: 1px solid var(--line); color: var(--muted); font-size: 0.72rem; }
.case-source a { color: var(--indigo-dark); font-weight: 700; }

.boundary-card {
  display: grid;
  grid-template-columns: 80px 1fr;
  gap: 1.5rem;
  align-items: center;
  padding: 2rem;
  border: 1px solid var(--crimson);
  background: var(--crimson-soft);
}

.boundary-card[data-status="design-dependent"] { border-color: var(--green); background: var(--green-soft); }
.boundary-card[data-status="unresolved"] { border-color: var(--amber); background: var(--amber-soft); }
.boundary-card > div:last-child > p:first-child { margin: 0; color: var(--muted); font-family: var(--mono); font-size: 0.68rem; text-transform: uppercase; }
.boundary-card h3 { margin: 0.25rem 0 0; font-family: var(--display); font-size: clamp(1.5rem, 3vw, 2.4rem); }
.boundary-card > div:last-child > p:last-child { max-width: 780px; margin: 0.5rem 0 0; color: #583b42; }
.boundary-card[data-status="design-dependent"] > div:last-child > p:last-child { color: #285641; }
.boundary-card[data-status="unresolved"] > div:last-child > p:last-child { color: #614b22; }
.boundary-signal { display: grid; gap: 0.45rem; }
.boundary-signal span { height: 5px; display: block; background: var(--crimson); transform-origin: left; }
.boundary-signal span:nth-child(2) { transform: scaleX(0.72); }
.boundary-signal span:nth-child(3) { transform: scaleX(0.42); }
.boundary-card[data-status="design-dependent"] .boundary-signal span { background: var(--green); }
.boundary-card[data-status="unresolved"] .boundary-signal span { background: var(--amber); }

.equivalence-card {
  display: grid;
  grid-template-columns: 1.2fr 1fr auto;
  gap: 2rem;
  align-items: center;
  margin-top: 1.4rem;
  padding: 1.7rem 2rem;
  border: 1px solid var(--line-strong);
  background: white;
}

.equivalence-card h3 { max-width: 430px; margin: 0; font-family: var(--display); font-size: 1.4rem; }
.equivalence-card dl { display: grid; grid-template-columns: repeat(2, 1fr); gap: 0.7rem 1.2rem; margin: 0; }
.equivalence-card dt { color: var(--muted); font-size: 0.65rem; }
.equivalence-card dd { margin: 0; font-family: var(--mono); font-size: 0.78rem; }
.equality-check { max-width: 130px; margin: 0; color: var(--green); font-size: 0.73rem; font-weight: 700; }
.equality-check span { width: 1.6rem; height: 1.6rem; display: grid; place-items: center; margin-bottom: 0.35rem; border-radius: 50%; color: white; background: var(--green); }

.comparison-table-wrap { margin-top: 2rem; overflow-x: auto; border-block: 1px solid var(--line-strong); }
table { width: 100%; border-collapse: collapse; font-size: 0.8rem; }
caption { padding: 0 0 0.7rem; color: var(--muted); font-family: var(--mono); font-size: 0.66rem; text-align: left; text-transform: uppercase; }
th, td { padding: 0.9rem 0.7rem; border-bottom: 1px solid var(--line); text-align: right; white-space: nowrap; }
th:first-child, td:first-child { padding-left: 0; text-align: left; }
th { color: var(--muted); font-family: var(--mono); font-size: 0.65rem; letter-spacing: 0.05em; text-transform: uppercase; }
td:not(:first-child) { font-family: var(--mono); }
tbody tr[data-selected="true"] { color: var(--indigo-dark); background: rgb(49 86 166 / 6%); }

.report-card {
  position: relative;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 1.5rem;
  align-items: center;
  margin-top: 2rem;
  padding: 1.7rem 2rem;
  color: white;
  background: var(--ink);
}

.report-card > div > p:last-child { max-width: 850px; margin: 0.35rem 0 0; color: #d9e4ee; font-family: var(--display); font-size: 1.18rem; line-height: 1.45; }
.report-card .eyebrow { color: var(--on-ink-muted); }
.report-card button { min-height: 42px; padding: 0.55rem 0.8rem; color: white; border: 1px solid #71869b; border-radius: 3px; background: transparent; cursor: pointer; font-size: 0.72rem; font-weight: 700; }
.report-card button:hover { background: rgb(255 255 255 / 8%); }
.copy-status { position: absolute; right: 2rem; bottom: 0.25rem; margin: 0; color: #a9c2da; font-size: 0.63rem; }

.checklist-grid { display: grid; grid-template-columns: repeat(4, 1fr); margin-top: 4rem; border-top: 1px solid var(--line-strong); }
.checklist-grid article { padding: 1.5rem; }
.checklist-grid article + article { border-left: 1px solid var(--line); }
.checklist-grid span { color: var(--cyan); font-family: var(--mono); font-size: 0.68rem; }
.checklist-grid h3 { margin: 1.8rem 0 0.5rem; font-family: var(--display); font-size: 1.15rem; }
.checklist-grid p { margin: 0; color: var(--muted); font-size: 0.78rem; }

.teach { border-top: 1px solid var(--line); }
.teaching-layout { display: grid; grid-template-columns: 1.35fr 0.65fr; gap: 1.4rem; }
.exercise-card, .facilitator-card { padding: clamp(1.6rem, 4vw, 3rem); border: 1px solid var(--line-strong); background: white; }
.exercise-card { box-shadow: var(--shadow); }
.exercise-card h3, .facilitator-card h3 { margin: 0.5rem 0 1rem; font-family: var(--display); font-size: 1.7rem; }
.exercise-card p:not(.card-kicker), .facilitator-card li { color: var(--muted); }
.exercise-card ol { margin: 1.7rem 0; padding-left: 1.3rem; }
.exercise-card li { margin: 0.65rem 0; padding-left: 0.4rem; }
.text-link { color: var(--indigo-dark); font-size: 0.78rem; font-weight: 750; }
.facilitator-card { background: #eaf0f7; }
.facilitator-card ul { margin: 0; padding: 0; list-style: none; }
.facilitator-card li { padding: 0.8rem 0; border-top: 1px solid var(--line); font-size: 0.83rem; }

.neighbors {
  display: grid;
  grid-template-columns: 1.1fr 1fr 1fr;
  gap: 1px;
  margin-bottom: 7rem;
  border: 1px solid var(--line-strong);
  background: var(--line);
}

.neighbors > * { padding: 2rem; background: white; }
.neighbors h2 { font-size: 2rem; }
.neighbors a { display: grid; align-content: center; text-decoration: none; }
.neighbors a:hover { background: #f8faff; }
.neighbors a strong { font-family: var(--display); font-size: 1.25rem; }
.neighbors a span { margin-top: 0.4rem; color: var(--muted); font-size: 0.78rem; }

footer {
  min-height: 120px;
  display: flex;
  justify-content: space-between;
  gap: 2rem;
  align-items: center;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.72rem;
}

footer p:last-child { text-align: right; }

@media (max-width: 900px) {
  .site-header { min-height: 78px; }
  .site-header nav { display: none; }
  .hero { grid-template-columns: 1fr; gap: 3rem; padding: 5rem 0; }
  .hero-proof { max-width: 520px; }
  .route-grid { grid-template-columns: 1fr 1fr; }
  .route-grid a:nth-child(3) { border-left: 0; border-top: 1px solid var(--line); }
  .route-grid a:nth-child(4) { border-top: 1px solid var(--line); }
  .concept-grid { grid-template-columns: 1fr; }
  .concept-grid article + article { border-left: 0; border-top: 1px solid var(--line); }
  .lab-shell { grid-template-columns: 1fr; }
  .controls { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.2rem; border-right: 0; border-bottom: 1px solid var(--line); }
  .control-heading { grid-column: 1 / -1; margin: 0; }
  .select-label { grid-column: 1 / -1; margin: 0; }
  .controls select { grid-column: 1 / -1; }
  .reset-button { grid-column: 1 / -1; margin: 0; }
  .equivalence-card { grid-template-columns: 1fr 1fr; }
  .equality-check { max-width: none; }
  .case-metrics { grid-template-columns: 1fr 1fr; }
  .case-metrics > div:nth-child(3) { border-left: 0; border-top: 1px solid var(--line); }
  .case-metrics > div:nth-child(4) { border-top: 1px solid var(--line); }
  .checklist-grid { grid-template-columns: 1fr 1fr; }
  .checklist-grid article:nth-child(3) { border-left: 0; border-top: 1px solid var(--line); }
  .checklist-grid article:nth-child(4) { border-top: 1px solid var(--line); }
  .neighbors { grid-template-columns: 1fr; }
}

@media (max-width: 620px) {
  body { font-size: 15px; }
  .hero { min-height: auto; padding: 4rem 0; }
  .hero h1 { font-size: clamp(3.2rem, 15vw, 4.5rem); }
  .route-grid { grid-template-columns: 1fr; }
  .route-grid a { min-height: 145px; }
  .route-grid a + a { border-left: 0; border-top: 1px solid var(--line); }
  .section { padding: 5.5rem 0; }
  .controls { grid-template-columns: 1fr; }
  .controls > * { grid-column: 1 !important; }
  .sample-summary strong { font-size: 1.3rem; }
  .sample-summary small { font-size: 0.6rem; }
  .method-picker { grid-template-columns: 1fr; }
  .method-picker button + button { border-left: 0; border-top: 1px solid var(--line); }
  .selected-method { grid-template-columns: 1fr; gap: 1rem; }
  .method-ledger dl { grid-template-columns: 1fr; }
  .boundary-card { grid-template-columns: 1fr; }
  .boundary-signal { width: 60px; }
  .equivalence-card { grid-template-columns: 1fr; }
  .equivalence-card dl { grid-template-columns: 1fr 1fr; }
  .report-card { grid-template-columns: 1fr; }
  .report-card button { justify-self: start; }
  .copy-status { position: static; }
  .case-metrics { grid-template-columns: 1fr; }
  .case-metrics > div + div { border-left: 0; border-top: 1px solid var(--line); }
  .case-boundary { grid-template-columns: 1fr; }
  .checklist-grid { grid-template-columns: 1fr; }
  .checklist-grid article + article { border-left: 0; border-top: 1px solid var(--line); }
  .teaching-layout { grid-template-columns: 1fr; }
  .neighbors > * { padding: 1.5rem; }
  footer { align-items: flex-start; flex-direction: column; padding: 2rem 0; }
  footer p { margin: 0; }
  footer p:last-child { text-align: left; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}

@media print {
  .site-header nav,
  .hero-actions,
  .controls,
  .method-picker,
  .report-card button,
  .copy-status { display: none; }
  body { background: white; color: black; }
  main, footer { width: 100%; }
  .hero { min-height: auto; padding: 2rem 0; }
  .run { width: 100%; margin: 0; padding: 2rem 0; background: white; }
  .lab-shell { display: block; box-shadow: none; }
  .lab-output { padding: 1rem; }
  .section { padding: 3rem 0; break-inside: avoid; }
}