:root {
  --obs-ink: #172039;
  --obs-paper: #fffefa;
  --obs-paper-cool: #f1f4f8;
  --obs-pearl: #e8edf5;
  --obs-line: #8997aa;
  --obs-graphite: #354052;
  --obs-deep: #101925;
  --obs-sapphire: #17347f;
  --obs-cobalt: #3a68cb;
  --obs-coral: #d96872;
  --obs-gold: #ffd27a;
  --obs-teal: #3d8178;
  --obs-phosphor: #8ee0c2;
  --obs-shadow: rgba(23, 32, 57, .24);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  min-width: 320px;
  margin: 0;
  color: var(--obs-ink);
  background:
    linear-gradient(rgba(23, 32, 57, .07) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 32, 57, .07) 1px, transparent 1px),
    #dce2ed;
  background-size: 24px 24px;
  font: 16px/1.65 Tahoma, Calibri, system-ui, sans-serif;
}

code, pre { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }

.observation-page {
  width: min(1180px, calc(100% - 32px));
  margin: 24px auto;
  overflow: hidden;
  background: var(--obs-paper);
  border: 1px solid #36455f;
  box-shadow: 0 28px 70px var(--obs-shadow);
}

.observation-hero {
  color: #fff;
  background:
    radial-gradient(circle at 83% 25%, rgba(255, 210, 122, .22), transparent 27%),
    radial-gradient(circle at 18% 86%, rgba(217, 104, 114, .26), transparent 32%),
    linear-gradient(132deg, var(--obs-sapphire), var(--obs-cobalt) 62%, #7d405e);
  border-bottom: 7px solid var(--obs-gold);
}

.observation-hero .hierarchy-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  padding: 18px clamp(22px, 5vw, 64px);
  color: #e7edff;
  background: rgba(10, 20, 48, .24);
  border-bottom: 1px solid rgba(255,255,255,.25);
  font-size: 12px;
}

.observation-hero .hierarchy-nav a { color: var(--obs-gold); font-weight: 750; text-decoration: none; }
.observation-hero .hierarchy-nav a:hover, .observation-hero .hierarchy-nav a:focus-visible { text-decoration: underline; text-underline-offset: 4px; }

.hero-layout {
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(280px, .55fr);
  gap: clamp(36px, 7vw, 90px);
  align-items: end;
  min-height: 620px;
  padding: clamp(54px, 9vw, 112px) clamp(24px, 6vw, 76px) clamp(60px, 8vw, 96px);
}

.observation-hero h1 {
  max-width: 790px;
  margin: 0;
  font-size: clamp(62px, 10vw, 126px);
  letter-spacing: -.06em;
  line-height: .82;
}

.page-deck {
  max-width: 760px;
  margin: 34px 0 0;
  color: #f0f3ff;
  font: clamp(20px, 2.2vw, 28px)/1.48 Georgia, serif;
}

.hero-record { margin: 0; border-top: 6px solid var(--obs-gold); box-shadow: 12px 12px 0 rgba(12, 20, 43, .22); }
.hero-record div { display: grid; grid-template-columns: 92px 1fr; gap: 14px; padding: 14px 16px; color: var(--obs-ink); background: rgba(255, 254, 250, .94); border-bottom: 1px solid #aab4c2; }
.hero-record dt { color: #4d5d74; font-size: 10px; font-weight: 800; letter-spacing: .11em; text-transform: uppercase; }
.hero-record dd { margin: 0; font-size: 13px; font-weight: 750; line-height: 1.4; }

.page-rail {
  display: flex;
  flex-wrap: wrap;
  gap: 1px;
  padding: 9px clamp(18px, 4vw, 48px);
  background: var(--obs-graphite);
  border-bottom: 1px solid #151d2b;
}

.page-rail a {
  padding: 8px 15px;
  color: #f4f6fb;
  background: #465267;
  border: 1px solid #657189;
  box-shadow: inset 0 1px rgba(255,255,255,.22), 0 2px 0 #222a38;
  font-size: 11px;
  font-weight: 800;
  letter-spacing: .08em;
  text-decoration: none;
  text-transform: uppercase;
}

.page-rail a:hover, .page-rail a:focus-visible { color: var(--obs-ink); background: var(--obs-gold); border-color: #f7e0a6; }
.page-rail a:active { transform: translateY(1px); box-shadow: inset 0 1px #222a38; }

.observation-body { width: min(1060px, calc(100% - 42px)); margin: 0 auto; }

.opening, .interaction, .measurement, .update, .implementation, .transformer, .limits {
  padding: clamp(62px, 9vw, 108px) 0;
  border-bottom: 1px solid var(--obs-line);
}

.opening {
  display: grid;
  grid-template-columns: minmax(260px, .72fr) minmax(0, 1.28fr);
  gap: clamp(36px, 7vw, 96px);
}

.opening h2, .section-copy h2, .limits h2, .research-ledger h2 {
  margin: 0;
  font-size: clamp(38px, 5.8vw, 70px);
  letter-spacing: -.045em;
  line-height: .98;
}

.opening-copy p { margin: 0 0 22px; font-size: 18px; line-height: 1.72; }
.opening-copy p:last-child { margin-bottom: 0; }

.section-copy { display: grid; grid-template-columns: minmax(280px, .9fr) minmax(0, 1.1fr); gap: clamp(34px, 7vw, 88px); align-items: start; margin-bottom: 42px; }
.section-copy p { max-width: 650px; margin: 3px 0 0; font-size: 18px; line-height: 1.7; }

.interaction-map {
  margin: 0;
  padding: clamp(20px, 4vw, 42px);
  color: #e8eef6;
  background: var(--obs-deep);
  border: 1px solid #465368;
  box-shadow: inset 0 1px rgba(255,255,255,.12), 12px 12px 0 rgba(23,32,57,.16);
}

.pass-label { display: flex; align-items: baseline; gap: 14px; margin-bottom: 16px; }
.pass-label span { color: var(--obs-phosphor); font-size: 11px; font-weight: 850; letter-spacing: .12em; text-transform: uppercase; }
.pass-label p { margin: 0; color: #b9c5d4; font-size: 13px; }

.forward-pass { display: grid; grid-template-columns: 1fr 30px 1.25fr 30px .72fr 36px 1.15fr 30px .8fr; align-items: center; gap: 6px; margin: 0; padding: 0; list-style: none; }
.transport-node, .nonlinear-node, .observed-node { min-width: 0; padding: 15px 12px; border: 1px solid #647087; text-align: center; }
.transport-node { background: #263143; }
.nonlinear-node { color: #172039; background: var(--obs-gold); border-color: #ffe5a6; box-shadow: 0 0 0 3px rgba(255,210,122,.12); }
.transport-node strong, .nonlinear-node strong, .observed-node strong { display: block; font-size: 14px; line-height: 1.25; }
.transport-node span, .nonlinear-node span, .observed-node small { display: block; margin-top: 6px; font-size: 9px; font-weight: 800; letter-spacing: .06em; line-height: 1.3; text-transform: uppercase; }
.transport-node span { color: #aeb9c8; }
.nonlinear-node span { color: #5f4a18; }
.flow-arrow, .split-arrow { color: #7d8aa0; font: 21px/1 Georgia, serif; text-align: center; }
.split-arrow { display: flex; flex-direction: column; gap: 9px; }
.branch-stack { display: grid; gap: 8px; }
.observed-node { display: block; color: #ecfff7; background: #225c56; border-color: #61a499; box-shadow: inset 4px 0 var(--obs-phosphor); }
.observed-node small { color: var(--obs-phosphor); }

.boundary-line { margin: 28px 0; border-top: 1px dashed #718097; text-align: center; }
.boundary-line span { position: relative; top: -11px; padding: 3px 11px; color: var(--obs-gold); background: var(--obs-deep); font-size: 11px; }

.backward-pass { display: grid; grid-template-columns: .8fr 1.4fr 1fr; gap: 12px; align-items: stretch; }
.backward-source, .backward-result, .backward-pair > div { display: flex; flex-direction: column; justify-content: center; min-height: 74px; padding: 13px 15px; border: 1px solid #536076; }
.backward-source, .backward-result { background: #202b3b; }
.backward-pair { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; }
.backward-pair > div { background: #163f3d; border-color: #47857d; }
.backward-pass code { color: #fff; font-size: 17px; }
.backward-pass span { margin-top: 5px; color: #aeb9c8; font-size: 10px; line-height: 1.35; }
.backward-pair span { color: #bfe0d7; }
.interaction-map figcaption { margin-top: 24px; padding-top: 17px; color: #aeb9c8; border-top: 1px solid #465368; font-size: 12px; line-height: 1.55; }

.boundary-essay { display: grid; grid-template-columns: minmax(230px, .58fr) minmax(0, 1.42fr); gap: clamp(32px, 6vw, 76px); margin-top: 58px; padding-top: 36px; border-top: 6px solid var(--obs-coral); }
.boundary-essay h3, .site-derivation h3, .runtime-contract > h3, .transformer-operational h3 { margin: 0; font: 27px/1.24 Georgia, serif; }
.boundary-essay p { margin: 0 0 20px; font-size: 16px; line-height: 1.7; }
.boundary-essay p:last-child { margin-bottom: 0; }

.site-derivation { display: grid; grid-template-columns: minmax(230px, .58fr) minmax(0, 1.42fr); gap: clamp(32px, 6vw, 76px); margin-top: 48px; padding: 32px 0; border-top: 1px solid var(--obs-line); border-bottom: 1px solid var(--obs-line); }
.site-derivation ol { margin: 0; padding: 0; list-style: none; counter-reset: sites; }
.site-derivation li { position: relative; margin: 0; padding: 0 0 19px 46px; font-size: 15px; line-height: 1.62; counter-increment: sites; }
.site-derivation li:last-child { padding-bottom: 0; }
.site-derivation li::before { position: absolute; left: 0; top: 1px; content: counter(sites, decimal-leading-zero); color: var(--obs-coral); font: 700 17px/1.4 ui-monospace, SFMono-Regular, Menlo, monospace; }

.measurement { margin: 0 calc(50% - 50vw); padding-right: max(21px, calc((100vw - 1060px) / 2)); padding-left: max(21px, calc((100vw - 1060px) / 2)); background: #eef1f7; }

.math-derivation { max-width: 890px; margin: 0 auto; padding: clamp(28px, 5vw, 54px); background: var(--obs-paper); border: 1px solid var(--obs-line); box-shadow: 10px 10px 0 rgba(23,32,57,.10); }
.math-derivation > p { max-width: 760px; margin: 0 auto 24px; font-size: 16px; line-height: 1.72; }
.math-derivation > p:last-child { margin-bottom: 0; }
.equation-display { max-width: 800px; margin: 32px auto; padding: 20px 24px; color: #eaf4f0; background: var(--obs-deep); border-left: 6px solid var(--obs-phosphor); }
.equation-display span { display: block; margin-bottom: 10px; color: var(--obs-gold); font-size: 10px; font-weight: 800; letter-spacing: .09em; text-transform: uppercase; }
.equation-display code { display: block; overflow-x: auto; color: #eafaf4; font-size: clamp(14px, 2vw, 20px); white-space: nowrap; }
.equation-display.equation-pair code + code { margin-top: 13px; padding-top: 13px; border-top: 1px solid #4d5b6d; }
.equation-display.equation-result { color: var(--obs-ink); background: #dfece7; border-left-color: var(--obs-teal); }
.equation-display.equation-result span { color: var(--obs-teal); }
.equation-display.equation-result code { color: var(--obs-ink); }

.measurement-note { display: grid; grid-template-columns: .7fr 1.3fr; gap: 28px; margin-top: 24px; padding: 24px 28px; color: #f4f7fc; background: var(--obs-graphite); border-top: 5px solid var(--obs-gold); }
.measurement-note strong { font: 22px/1.35 Georgia, serif; }
.measurement-note p { margin: 0; color: #dce3ed; font-size: 14px; line-height: 1.6; }

.update-stack { margin: 0; padding: 0; border-top: 1px solid var(--obs-line); list-style: none; }
.update-stack li { display: grid; grid-template-columns: 64px 1fr; gap: 22px; padding: 24px 12px; border-bottom: 1px solid var(--obs-line); }
.update-stack li > span { color: var(--obs-coral); font: 700 31px/1 Georgia, serif; text-align: center; }
.update-stack h3 { margin: 0 0 7px; font-size: 22px; }
.update-stack p { max-width: 800px; margin: 0; color: #4b5768; font-size: 15px; line-height: 1.58; }
.update-stack code { padding: 1px 4px; background: #e8edf5; }
.update-stack .update-observed { background: #e3efea; box-shadow: inset 7px 0 var(--obs-teal); }

.update-exposition { columns: 2; column-gap: clamp(34px, 6vw, 74px); margin-bottom: 44px; padding-bottom: 38px; border-bottom: 1px solid var(--obs-line); }
.update-exposition p { break-inside: avoid; margin: 0 0 20px; font-size: 16px; line-height: 1.7; }

.mixture-instrument { margin-top: 36px; padding: clamp(24px, 4vw, 42px); color: #e6edf6; background: var(--obs-deep); border: 1px solid #4e5b6d; box-shadow: inset 0 1px rgba(255,255,255,.12); }
.instrument-scale, .instrument-ends { display: flex; justify-content: space-between; gap: 30px; }
.instrument-scale { color: #aab7c8; font-size: 11px; letter-spacing: .08em; text-transform: uppercase; }
.instrument-track { position: relative; height: 22px; margin: 12px 0 18px; background: linear-gradient(90deg, var(--obs-cobalt), var(--obs-phosphor)); border: 1px solid #8a9bae; box-shadow: inset 0 4px 8px rgba(0,0,0,.32); }
.instrument-track i { position: absolute; top: -5px; left: 60%; width: 6px; height: 30px; background: var(--obs-gold); border: 1px solid #fff1c7; box-shadow: 0 0 0 3px rgba(255,210,122,.16); }
.instrument-track b { position: absolute; right: 10px; top: 1px; color: #10202b; font-size: 9px; letter-spacing: .08em; text-transform: uppercase; }
.instrument-ends > div { max-width: 320px; }
.instrument-ends strong, .instrument-ends span { display: inline-block; margin-right: 10px; }
.instrument-ends strong { color: var(--obs-gold); }
.instrument-ends span { color: var(--obs-phosphor); }
.instrument-ends p { margin: 5px 0 0; color: #b9c5d4; font-size: 12px; }

.implementation { margin: 0 calc(50% - 50vw); padding-right: max(21px, calc((100vw - 1060px) / 2)); padding-left: max(21px, calc((100vw - 1060px) / 2)); background: #e6ebf3; }
.code-panel { overflow: hidden; background: #0d1520; border: 1px solid #536176; box-shadow: 12px 12px 0 rgba(23,32,57,.15); }
.code-title { display: flex; justify-content: space-between; gap: 24px; padding: 12px 18px; color: #dce4ee; background: #354052; border-bottom: 1px solid #607087; font-size: 10px; font-weight: 800; letter-spacing: .08em; text-transform: uppercase; }
.code-panel pre { margin: 0; padding: clamp(22px, 4vw, 42px); overflow-x: auto; color: #dff7ee; font-size: 13px; line-height: 1.65; tab-size: 4; }
.code-panel-spaced { margin-top: 30px; }

.mechanism-reading { max-width: 850px; margin: 0 auto 44px; columns: 2; column-gap: clamp(34px, 6vw, 72px); }
.mechanism-reading p { break-inside: avoid; margin: 0 0 20px; font-size: 16px; line-height: 1.68; }

.runtime-contract { display: grid; grid-template-columns: minmax(220px, .55fr) minmax(0, 1.45fr); gap: clamp(32px, 6vw, 72px); margin-top: 54px; padding-top: 34px; border-top: 6px solid var(--obs-coral); }
.runtime-contract dl { margin: 0; border-top: 1px solid var(--obs-line); }
.runtime-contract dl div { display: grid; grid-template-columns: 150px 1fr; gap: 24px; padding: 18px 0; border-bottom: 1px solid var(--obs-line); }
.runtime-contract dt { color: var(--obs-sapphire); font-size: 12px; font-weight: 850; letter-spacing: .05em; text-transform: uppercase; }
.runtime-contract dd { margin: 0; font-size: 14px; line-height: 1.62; }

.transformer-map {
  display: grid;
  grid-template-columns: repeat(5, minmax(110px, 1fr) 22px) minmax(150px, 1.2fr);
  align-items: center;
  gap: 7px;
  padding: 24px;
  color: #e6edf6;
  background: var(--obs-deep);
  border: 1px solid #4e5b6d;
  box-shadow: inset 0 1px rgba(255,255,255,.12), 10px 10px 0 rgba(23,32,57,.14);
}
.transformer-map > div { min-height: 105px; padding: 16px 13px; background: #253143; border: 1px solid #5b687d; }
.transformer-map > i { color: #8593a8; font: 18px/1 Georgia, serif; text-align: center; }
.transformer-map span, .transformer-map small { display: block; font-size: 9px; font-style: normal; font-weight: 800; letter-spacing: .07em; line-height: 1.35; text-transform: uppercase; }
.transformer-map span { color: #aeb9c8; }
.transformer-map strong { display: block; margin: 8px 0; color: #fff; font-size: 14px; line-height: 1.25; }
.transformer-map small { color: var(--obs-gold); }
.transformer-map .transformer-observed { background: #205850; border-color: #65a99d; box-shadow: inset 5px 0 var(--obs-phosphor); }
.transformer-map .transformer-observed small { color: var(--obs-phosphor); }

.transformer-exposition { max-width: 850px; margin: 50px auto 0; columns: 2; column-gap: clamp(34px, 6vw, 72px); }
.transformer-exposition p { break-inside: avoid; margin: 0 0 20px; font-size: 16px; line-height: 1.68; }

.transformer-operational { display: grid; grid-template-columns: minmax(220px, .55fr) minmax(0, 1.45fr); gap: clamp(32px, 6vw, 72px); margin-top: 52px; padding: 34px 0; border-top: 1px solid var(--obs-line); border-bottom: 1px solid var(--obs-line); }
.transformer-operational p { grid-column: 2; margin: 0 0 18px; font-size: 15px; line-height: 1.66; }
.transformer-operational p:last-child { margin-bottom: 0; }

.limits { display: grid; grid-template-columns: .75fr 1.25fr; gap: clamp(36px, 7vw, 90px); }
.limits > div p { margin: 0 0 20px; font-size: 17px; line-height: 1.7; }
.limits > div p:last-child { margin-bottom: 0; }

.research-ledger { display: grid; grid-template-columns: .8fr 1.2fr; gap: clamp(36px, 7vw, 88px); margin: 0 calc(50% - 50vw); padding: clamp(48px, 7vw, 84px) max(21px, calc((100vw - 1060px) / 2)); color: #f4f6fb; background: var(--obs-graphite); }
.research-ledger h2 { font-size: clamp(36px, 5vw, 58px); }
.research-ledger p { color: #d8e0eb; font-size: 15px; }
.research-ledger nav { align-self: center; border-top: 1px solid #768298; }
.research-ledger a { display: grid; grid-template-columns: 130px 1fr; gap: 18px; padding: 14px 0; color: #fff; border-bottom: 1px solid #768298; text-decoration: none; }
.research-ledger a:hover, .research-ledger a:focus-visible { color: var(--obs-gold); }
.research-ledger a span { color: var(--obs-phosphor); font-size: 10px; letter-spacing: .06em; text-transform: uppercase; }
.research-ledger a strong { font-size: 13px; }

:focus-visible { outline: 3px solid var(--obs-gold); outline-offset: 3px; }

@media (max-width: 900px) {
  .hero-layout, .opening, .section-copy, .boundary-essay, .site-derivation, .runtime-contract, .transformer-operational, .limits, .research-ledger { grid-template-columns: 1fr; }
  .hero-layout { min-height: 0; }
  .hero-record { max-width: 520px; }
  .forward-pass { grid-template-columns: 1fr; }
  .flow-arrow { transform: rotate(90deg); }
  .split-arrow { flex-direction: row; justify-content: center; transform: rotate(90deg); }
  .branch-stack { grid-template-columns: 1fr 1fr; }
  .transformer-operational p { grid-column: 1; }
  .transformer-map { grid-template-columns: 1fr; }
  .transformer-map > i { transform: rotate(90deg); }
}

@media (max-width: 620px) {
  .observation-page { width: 100%; margin: 0; border-inline: 0; }
  .observation-body { width: min(100% - 28px, 1060px); }
  .observation-hero h1 { font-size: clamp(55px, 18vw, 82px); }
  .hero-layout { padding-top: 56px; }
  .page-rail { position: static; }
  .branch-stack, .backward-pass, .backward-pair { grid-template-columns: 1fr; }
  .measurement-note { grid-template-columns: 1fr; }
  .update-exposition, .mechanism-reading, .transformer-exposition { columns: 1; }
  .update-stack li { grid-template-columns: 42px 1fr; gap: 12px; padding-inline: 0; }
  .instrument-ends { flex-direction: column; }
  .code-title { flex-direction: column; gap: 3px; }
  .runtime-contract dl div { grid-template-columns: 1fr; gap: 6px; }
  .research-ledger a { grid-template-columns: 1fr; gap: 3px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

@media (prefers-contrast: more) {
  .observation-page { border-width: 2px; }
  .transport-node, .nonlinear-node, .observed-node { border-width: 2px; }
}