@import url('https://fonts.googleapis.com/css2?family=DM+Sans:wght@400;500;600;700&family=Noto+Sans+KR:wght@400;500;600;700;900&display=swap');

:root {
  --ink: #111923;
  --ink-soft: #34414f;
  --paper: #f2efe6;
  --paper-bright: #fbf8ef;
  --orange: #ff5c35;
  --orange-dark: #ad2f14;
  --blue: #5274ff;
  --sky: #9ebef2;
  --rule: rgba(17, 25, 35, .18);
  --shadow: 0 24px 70px rgba(17, 25, 35, .12);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: "DM Sans", "Noto Sans KR", system-ui, sans-serif;
  line-height: 1.6;
  overflow-x: hidden;
}
button, input, summary { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
a { color: inherit; }
svg { display: block; width: 100%; height: 100%; }
em { font-style: normal; }

.skip-link {
  position: fixed; left: 16px; top: -80px; z-index: 100;
  padding: 12px 18px; background: var(--orange); color: white;
}
.skip-link:focus { top: 16px; }

.site-header {
  position: sticky; top: 0; z-index: 50; height: 72px;
  display: grid; grid-template-columns: 1fr auto 1fr; align-items: center;
  padding: 0 4vw; color: white; background: rgba(16, 23, 34, .92);
  border-bottom: 1px solid rgba(255,255,255,.14); backdrop-filter: blur(14px);
}
.brand { display: inline-flex; width: max-content; align-items: center; gap: 11px; text-decoration: none; font-weight: 800; letter-spacing: -.04em; }
.brand-mark { position: relative; display: inline-flex; gap: 3px; width: 27px; height: 18px; }
.brand-mark i { position: relative; display: block; width: 12px; height: 18px; border: 2px solid currentColor; border-radius: 60% 18% 60% 18%; transform: rotate(45deg); }
.brand-mark i:last-child { transform: rotate(225deg); }
.brand-mark::after { content: ""; position: absolute; width: 4px; height: 4px; border-radius: 50%; background: var(--orange); left: 11px; top: 7px; }
.site-nav { display: flex; align-items: center; gap: clamp(18px, 3vw, 48px); font-size: 13px; }
.site-nav a { color: rgba(255,255,255,.68); text-decoration: none; transition: color .2s ease; }
.site-nav a:hover, .site-nav a:focus-visible { color: white; }
.header-progress { justify-self: end; display: flex; align-items: center; gap: 12px; font-size: 12px; letter-spacing: .06em; }
.header-progress progress { appearance: none; display: block; width: 90px; height: 2px; border: 0; background: rgba(255,255,255,.22); }
.header-progress progress::-webkit-progress-bar { background: rgba(255,255,255,.22); }
.header-progress progress::-webkit-progress-value { background: var(--orange); transition: width .35s ease; }
.header-progress progress::-moz-progress-bar { background: var(--orange); }

.hero {
  position: relative; min-height: calc(100svh - 72px); padding: clamp(74px, 10vw, 138px) 7vw 70px;
  display: grid; grid-template-columns: minmax(0, 1.3fr) minmax(330px, .7fr); align-items: center;
  color: white; background: var(--ink); overflow: hidden;
}
.hero-grid {
  position: absolute; inset: 0; opacity: .13;
  background-image: linear-gradient(rgba(255,255,255,.23) 1px, transparent 1px), linear-gradient(90deg, rgba(255,255,255,.23) 1px, transparent 1px);
  background-size: 62px 62px; mask-image: linear-gradient(to right, black, transparent 82%);
}
.hero::before { content: ""; position: absolute; width: 42vw; height: 42vw; min-width: 520px; min-height: 520px; right: -10vw; top: 10%; border-radius: 50%; background: radial-gradient(circle, rgba(82,116,255,.45), transparent 67%); filter: blur(12px); }
.hero-copy { position: relative; z-index: 2; max-width: 930px; }
.eyebrow, .section-kicker { margin: 0 0 24px; font-size: 12px; font-weight: 700; letter-spacing: .22em; text-transform: uppercase; }
.eyebrow { color: var(--sky); }
.hero h1 { margin: 0; max-width: 920px; font-family: "Noto Sans KR", sans-serif; font-size: clamp(48px, 7.2vw, 112px); font-weight: 900; line-height: .98; letter-spacing: -.075em; }
.hero h1 em { color: var(--orange); }
.hero-lede { max-width: 600px; margin: 38px 0 0; color: rgba(255,255,255,.7); font-size: clamp(16px, 1.3vw, 20px); line-height: 1.75; word-break: keep-all; }
.hero-actions { display: flex; align-items: center; gap: 24px; margin-top: 36px; }
.button {
  appearance: none; min-height: 48px; padding: 12px 20px; border: 1px solid transparent; border-radius: 0;
  display: inline-flex; align-items: center; justify-content: center; gap: 8px; cursor: pointer;
  text-decoration: none; font-size: 14px; font-weight: 700; transition: transform .18s ease, background .18s ease, color .18s ease, border-color .18s ease;
}
.button:hover { transform: translateY(-2px); }
.button:active { transform: translateY(0); }
.button-primary { background: var(--orange); color: white; }
.button-primary:hover { background: #ff7656; }
.button-dark { background: var(--ink); color: white; }
.button-dark:hover { background: #263341; }
.button-quiet { border-color: var(--rule); background: transparent; color: var(--ink); }
.button-quiet:hover { border-color: var(--ink); }
.button-light { background: white; color: var(--ink); }
.key-guide { color: rgba(255,255,255,.56); font-size: 12px; }
kbd { min-width: 24px; padding: 3px 6px; border: 1px solid currentColor; border-bottom-width: 2px; color: inherit; background: rgba(255,255,255,.08); font-family: inherit; font-size: 10px; text-align: center; }
.hero-visual { position: relative; z-index: 1; height: min(560px, 52vw); min-height: 380px; }
.orbit { position: absolute; border: 1px solid rgba(255,255,255,.3); border-radius: 50%; }
.orbit::before, .orbit::after { content: ""; position: absolute; border-radius: 50%; background: var(--orange); }
.orbit-one { width: 390px; height: 390px; right: 2%; top: 8%; }
.orbit-one::before { width: 72px; height: 72px; left: -36px; top: 155px; }
.orbit-one span { position: absolute; inset: 46px; border: 44px solid rgba(255,255,255,.07); border-right-color: rgba(82,116,255,.7); border-radius: 50%; transform: rotate(-20deg); }
.orbit-two { width: 210px; height: 210px; right: 32%; bottom: 0; border-color: rgba(255,255,255,.17); }
.orbit-two::after { width: 34px; height: 34px; right: -17px; top: 88px; background: var(--sky); }
.hero-cross { position: absolute; right: 27%; top: 45%; transform: translate(50%,-50%); color: white; font-size: 32px; font-weight: 200; }
.hero-visual p { position: absolute; right: 0; bottom: 20px; margin: 0; color: rgba(255,255,255,.5); font-size: 12px; letter-spacing: .16em; text-transform: uppercase; writing-mode: vertical-rl; }
.scroll-note { position: absolute; left: 4vw; bottom: 30px; margin: 0; display: flex; align-items: center; gap: 12px; color: rgba(255,255,255,.36); font-size: 9px; letter-spacing: .18em; transform: rotate(-90deg); transform-origin: left center; }
.scroll-note span { width: 46px; height: 1px; background: currentColor; }

.guide { padding: 100px 7vw; display: grid; grid-template-columns: .8fr 1.2fr; gap: 7vw; background: var(--paper-bright); border-bottom: 1px solid var(--rule); }
.section-kicker { color: var(--orange-dark); }
.guide h2, .experiments-heading h2, .completion h2 { margin: 0; font-family: "Noto Sans KR", sans-serif; font-weight: 900; line-height: 1.08; letter-spacing: -.055em; }
.guide h2 { font-size: clamp(34px, 4.4vw, 64px); }
.guide-steps { margin: 4px 0 0; padding: 0; list-style: none; border-top: 1px solid var(--ink); }
.guide-steps li { display: grid; grid-template-columns: 54px 120px 1fr; gap: 10px; align-items: baseline; padding: 22px 0; border-bottom: 1px solid var(--rule); }
.guide-steps span { color: var(--orange-dark); font-size: 11px; }
.guide-steps strong { font-size: 17px; }
.guide-steps p { margin: 0; color: var(--ink-soft); font-size: 14px; }
.comfort-note { grid-column: 1 / -1; display: flex; align-items: center; gap: 16px; max-width: 840px; margin-top: 30px; padding: 18px 22px; border: 1px solid var(--rule); }
.comfort-note > span { display: grid; flex: 0 0 30px; width: 30px; height: 30px; place-items: center; border-radius: 50%; background: var(--ink); color: white; font-weight: 800; }
.comfort-note p { margin: 0; color: var(--ink-soft); font-size: 13px; }
.comfort-note strong { color: var(--ink); margin-right: 10px; }

.experiments-heading { padding: 130px 7vw 90px; display: grid; grid-template-columns: 1fr 1fr; background: var(--paper); }
.experiments-heading .section-kicker { grid-column: 1 / -1; }
.experiments-heading h2 { font-size: clamp(50px, 7vw, 104px); }
.experiments-heading > p:last-child { align-self: end; justify-self: end; max-width: 300px; color: var(--ink-soft); }

.experiment { position: relative; padding: 100px 7vw 72px; border-top: 1px solid var(--ink); background: var(--paper-bright); scroll-margin-top: 70px; }
.experiment:nth-of-type(odd) { background: var(--paper); }
.experiment::before { content: ""; position: absolute; left: 0; top: 0; width: 0; height: 4px; background: var(--orange); transition: width .5s ease; }
.experiment.is-complete::before { width: 100%; }
.experiment.is-complete .experiment-no::after { content: "✓"; margin-left: 9px; color: var(--orange-dark); }
.experiment-head { display: grid; grid-template-columns: minmax(110px,.28fr) minmax(260px,.72fr) minmax(320px,1fr); gap: 36px; align-items: start; margin-bottom: 50px; }
.experiment-no { font-size: 12px; font-weight: 800; letter-spacing: .1em; }
.experiment-type, .year { margin: 6px 0 0; color: #59636c; font-size: 12px; }
.experiment-head h2 { margin: 0; font-family: "Noto Sans KR", sans-serif; font-size: clamp(30px, 3.2vw, 48px); line-height: 1.1; letter-spacing: -.045em; }
.experiment-intro { max-width: 590px; margin: 0; color: var(--ink-soft); font-size: clamp(15px, 1.35vw, 19px); line-height: 1.8; word-break: keep-all; }
.experiment-intro em { color: var(--orange-dark); font-weight: 700; }
.lab-layout { display: grid; grid-template-columns: minmax(0, 1.55fr) minmax(280px, .45fr); gap: clamp(28px, 5vw, 78px); align-items: center; }
.lab-layout-flip { grid-template-columns: minmax(280px, .45fr) minmax(0, 1.55fr); }
.lab-layout-flip .stage { grid-column: 2; grid-row: 1; }
.lab-layout-flip .lab-controls { grid-column: 1; grid-row: 1; }
.stage { position: relative; width: 100%; min-height: 370px; overflow: hidden; background: #e8e4da; border: 1px solid rgba(17,25,35,.12); box-shadow: var(--shadow); }
.stage:focus-visible { outline: 4px solid var(--blue); outline-offset: 4px; }
.stage-dark { background: var(--ink); }
.lab-controls { display: flex; flex-direction: column; align-items: stretch; gap: 18px; }
.lab-controls label, .choice-group legend { display: flex; width: 100%; justify-content: space-between; color: var(--ink); font-size: 13px; font-weight: 700; }
.control-row { display: flex; flex-wrap: wrap; gap: 10px; }
.control-row .button { flex: 1 1 auto; }
.result { min-height: 54px; margin: 2px 0 0; padding-top: 16px; border-top: 1px solid var(--rule); color: var(--ink-soft); font-size: 13px; line-height: 1.65; }
.result strong { color: var(--ink); }
.choice-group { margin: 0 0 4px; padding: 0; border: 0; display: grid; grid-template-columns: repeat(3, 1fr); gap: 6px; }
.choice-group legend { grid-column: 1 / -1; margin-bottom: 10px; }
.choice-group button { min-height: 44px; border: 1px solid var(--rule); background: transparent; cursor: pointer; font-weight: 700; font-size: 13px; }
.choice-group button:hover, .choice-group button:focus-visible { border-color: var(--ink); }
.choice-group button[aria-pressed="true"] { border-color: var(--ink); background: var(--ink); color: white; }
.choice-group:disabled { opacity: .42; }
.choice-group:disabled button { cursor: not-allowed; }
.why { margin: 54px 0 0 calc(28% + 36px); border-top: 1px solid var(--rule); }
.why summary { position: relative; padding: 18px 40px 18px 0; cursor: pointer; font-size: 13px; font-weight: 800; list-style: none; }
.why summary::-webkit-details-marker { display: none; }
.why summary::after { content: "+"; position: absolute; right: 4px; top: 13px; font-size: 22px; font-weight: 400; }
.why[open] summary::after { content: "−"; }
.why p { max-width: 760px; margin: 0; padding: 0 0 24px; color: var(--ink-soft); font-size: 14px; line-height: 1.8; }

/* 01 Müller–Lyer */
.muller-stage svg { min-height: 370px; }
.illusion-line { fill: none; stroke: #f7f2df; stroke-width: 5; stroke-linecap: round; stroke-linejoin: round; }
.bottom-line { stroke: var(--orange); }
.muller-stage .top-line, .muller-stage .bottom-line { transition: transform .8s cubic-bezier(.22,.82,.24,1); }
.muller-stage .muller-wings { transition: opacity .3s ease .52s; }
.muller-overlap { opacity: 0; fill: var(--orange); stroke: #f7f2df; stroke-width: 2; text-anchor: middle; font-size: 13px; transition: opacity .28s ease; }
.muller-overlap text { stroke: none; fill: #a9bdd0; letter-spacing: .04em; }
.muller-stage.is-merged .top-line { transform: translateY(54px); }
.muller-stage.is-merged .bottom-line { transform: translateY(-54px); }
.muller-stage.is-merged .muller-wings { opacity: 0; }
.muller-stage.is-merged .muller-overlap { opacity: 1; transition-delay: .78s; }

/* 02 Ebbinghaus */
.ebb-stage { background: #d8d7ca; }
.ebb-surrounds { transition: opacity .45s ease, transform .55s ease; transform-origin: center; }
.ebb-targets circle { transition: transform .82s cubic-bezier(.22,.82,.24,1) .18s; }
.ebb-overlap { opacity: 0; fill: none; stroke: var(--orange-dark); stroke-width: 2; text-anchor: middle; font-size: 13px; transition: opacity .3s ease; }
.ebb-overlap text { fill: var(--ink); stroke: none; }
.ebb-stage.is-revealed .ebb-surrounds { opacity: 0; transform: scale(.72); }
.ebb-stage.is-revealed .ebb-targets circle:first-child { transform: translateX(170px); }
.ebb-stage.is-revealed .ebb-targets circle:last-child { transform: translateX(-170px); }
.ebb-stage.is-revealed .ebb-overlap { opacity: 1; transition-delay: .92s; }

/* 03 Café wall */
.cafe-stage { min-height: 400px; display: grid; place-items: center; padding: 38px 0; background: #0f1720; }
.cafe-grid { position: relative; width: calc(100% + 56px); padding: 3px 0; overflow: hidden; background: rgb(var(--mortar, 128), var(--mortar, 128), var(--mortar, 128)); }
.cafe-row { display: flex; width: calc(100% + 100px); height: 43px; margin-bottom: 5px; }
.cafe-row:last-child { margin-bottom: 0; }
.cafe-row:nth-child(even) { transform: translateX(-25px); }
.cafe-tile { flex: 0 0 50px; height: 43px; background: #f4efdd; }
.cafe-tile:nth-child(even) { background: #121a24; }
.cafe-tile { transition: opacity .38s ease, transform .48s cubic-bezier(.22,.82,.24,1); }
.cafe-guides { position: absolute; inset: 38px 0; opacity: 0; pointer-events: none; transition: opacity .25s ease; }
.cafe-guides i { position: absolute; left: 3%; right: 3%; height: 1px; background: var(--orange); box-shadow: 0 0 0 1px rgba(17,25,35,.35); }
.cafe-guides i:nth-child(1) { top: 48px; }.cafe-guides i:nth-child(2) { top: 96px; }.cafe-guides i:nth-child(3) { top: 144px; }.cafe-guides i:nth-child(4) { top: 192px; }.cafe-guides i:nth-child(5) { top: 240px; }
.cafe-stage.is-guided .cafe-guides { opacity: 1; }
.cafe-stage.is-guided .cafe-tile { opacity: .06; transform: scale(.72); }

/* 04 Simultaneous contrast */
.contrast-stage { display: grid; grid-template-columns: 1fr 1fr; }
.contrast-half { display: grid; place-items: center; transition: background-color .55s ease; }
.contrast-half.light { background: #eae6da; }
.contrast-half.dark { background: #25303b; }
.contrast-chip { position: absolute; z-index: 2; top: 50%; display: grid; width: 90px; height: 90px; place-items: center; color: white; background: #81898b; font-size: 13px; font-weight: 800; transform: translate(-50%, -50%); transition: left .82s cubic-bezier(.22,.82,.24,1); }
.contrast-half.light .contrast-chip { left: 25%; }
.contrast-half.dark .contrast-chip { left: 75%; transition-delay: .12s; }
.contrast-bridge { position: absolute; z-index: 3; width: 108px; height: 108px; left: 50%; top: 50%; border: 2px solid var(--orange); opacity: 0; transform: translate(-50%, -50%) scale(.75); transition: opacity .25s ease, transform .35s ease; pointer-events: none; }
.contrast-bridge::after { content: "A = B · 완전히 포개짐"; position: absolute; width: 190px; left: 50%; top: calc(100% + 18px); transform: translateX(-50%); color: var(--ink); font-size: 11px; font-weight: 800; text-align: center; }
.contrast-stage.is-revealed .contrast-half.light { background: #d6d4cb; }
.contrast-stage.is-revealed .contrast-half.dark { background: #48525a; }
.contrast-stage.is-revealed .contrast-chip { left: 50%; }
.contrast-stage.is-revealed .contrast-bridge { opacity: 1; transform: translate(-50%, -50%) scale(1); transition-delay: .92s; }

/* 05 Grid */
.grid-stage { display: grid; place-items: center; min-height: 430px; padding: 30px; }
.scint-grid { width: 100%; height: 100%; min-height: 370px; background-color: #11151b; background-image: radial-gradient(circle at 7px 7px, #fff 0 5px, transparent 6px), linear-gradient(#7d8790 14px, transparent 14px), linear-gradient(90deg, #7d8790 14px, transparent 14px); background-size: var(--grid-size, 58px) var(--grid-size, 58px); background-position: 0 0; transition: background-size .15s ease; }
.scint-grid.no-discs { background-image: linear-gradient(#7d8790 14px, transparent 14px), linear-gradient(90deg, #7d8790 14px, transparent 14px); }
.fixation { position: absolute; left: 50%; top: 50%; transform: translate(-50%,-50%); display: grid; width: 34px; height: 34px; place-items: center; color: var(--orange); font-size: 26px; font-weight: 400; text-shadow: 0 1px 3px rgba(0,0,0,.5); }
.fixation.small { width: 22px; height: 22px; font-size: 18px; }

/* 06 Zöllner */
.zollner-stage { min-height: 410px; background: #d9e0dc; }
.zollner-long { stroke: var(--ink); stroke-width: 4; }
.zollner-short { stroke: var(--blue); stroke-width: 2.5; stroke-linecap: round; transform-box: fill-box; transform-origin: center; transition: opacity .42s ease, transform .48s cubic-bezier(.22,.82,.24,1); }
.zollner-guide { stroke: var(--orange); stroke-width: 1.5; stroke-dasharray: 8 7; opacity: 0; transition: opacity .2s ease; }
.zollner-stage.is-guided .zollner-guide { opacity: 1; }
.zollner-stage.is-guided .zollner-short { opacity: .04; transform: scale(.2); }

/* 07 Troxler */
.troxler-stage { min-height: 470px; background: #d8ded8; }
.trox-dot { position: absolute; width: 94px; height: 94px; border-radius: 50%; filter: blur(15px); opacity: .56; }
.trox-dot.d1 { left: 13%; top: 16%; background: #ff6b4a; }.trox-dot.d2 { right: 14%; top: 19%; background: #5375ff; }.trox-dot.d3 { left: 18%; bottom: 12%; background: #57a987; }.trox-dot.d4 { right: 19%; bottom: 13%; background: #e1a235; }.trox-dot.d5 { left: 49%; top: 10%; width: 64px; height: 64px; background: #9d64bc; }
.troxler-stage .fixation { color: var(--ink); text-shadow: none; }
.trox-outline { position: absolute; inset: 8%; border: 1px dashed transparent; pointer-events: none; }
.troxler-stage.show-proof .trox-dot { outline: 2px solid var(--orange); filter: blur(7px); opacity: .8; }
.timer { display: flex; align-items: baseline; gap: 6px; }
.timer strong { font-size: 42px; line-height: 1; font-variant-numeric: tabular-nums; letter-spacing: -.05em; }
.timer span { color: var(--ink-soft); font-size: 12px; }

/* 08 Rubin */
.rubin-stage { min-height: 470px; background: #f8f5eb; }
.rubin-bg { fill: #f7f3e8; transition: fill .3s ease; }
.rubin-vase { fill: var(--ink); transition: fill .3s ease; }
.rubin-rim { fill: none; stroke: #f7f3e8; stroke-width: 4; transition: stroke .3s ease; }
.rubin-stage.is-flipped .rubin-bg { fill: var(--ink); }
.rubin-stage.is-flipped .rubin-vase { fill: #f7f3e8; }
.rubin-stage.is-flipped .rubin-rim { stroke: var(--ink); }

/* 09 Kanizsa */
.kanizsa-stage { min-height: 460px; background: #f5f1e6; }
.kanizsa-pacmen circle { fill: var(--ink); }
.kanizsa-pacmen .cutout { fill: #f5f1e6; }
.kanizsa-piece { transform-box: fill-box; transform-origin: center; transition: opacity .42s ease, transform .78s cubic-bezier(.22,.82,.24,1); }
.kanizsa-proof { fill: none; stroke: var(--orange); stroke-width: 3; stroke-linejoin: round; stroke-dasharray: 1; stroke-dashoffset: 1; opacity: 0; transition: opacity .12s ease, stroke-dashoffset .82s ease; }
.kanizsa-stage.is-outlining .kanizsa-proof,
.kanizsa-stage.is-cleared .kanizsa-proof { opacity: 1; stroke-dashoffset: 0; }
.kanizsa-stage.is-cleared .k-top { opacity: 0; transform: translateY(-90px) rotate(-12deg); }
.kanizsa-stage.is-cleared .k-left { opacity: 0; transform: translate(-95px, 58px) rotate(-14deg); }
.kanizsa-stage.is-cleared .k-right { opacity: 0; transform: translate(95px, 58px) rotate(14deg); }

/* 10 Ponzo */
.ponzo-stage { min-height: 470px; }
.ponzo-context { stroke: rgba(255,255,255,.68); stroke-width: 3; transition: opacity .48s ease, transform .65s ease; transform-origin: center; }
.ponzo-target { stroke: var(--orange); stroke-width: 8; stroke-linecap: round; }
.ponzo-top, .ponzo-bottom { transition: transform .82s cubic-bezier(.22,.82,.24,1) .14s; }
.ponzo-overlap { opacity: 0; fill: var(--orange); stroke: white; stroke-width: 2; text-anchor: middle; font-size: 13px; transition: opacity .28s ease; }
.ponzo-overlap text { fill: white; stroke: none; }
.ponzo-stage.is-merged .ponzo-context { opacity: .08; transform: scale(.94); }
.ponzo-stage.is-merged .ponzo-top { transform: translateY(86.5px); }
.ponzo-stage.is-merged .ponzo-bottom { transform: translateY(-86.5px); }
.ponzo-stage.is-merged .ponzo-overlap { opacity: 1; transition-delay: .92s; }

/* 11 Checker shadow */
.checker-stage { min-height: 500px; background: radial-gradient(circle at 50% 12%, #cad6d3, #78939a 78%); }
.checker-floor { fill: #779199; }
.checker-board { transition: opacity .5s ease, transform .72s cubic-bezier(.22,.82,.24,1); transform-origin: center; }
.checker-cell { stroke: rgba(18,29,31,.22); stroke-width: 1; }
.checker-light { fill: #e8eadc; }.checker-dark { fill: #737b77; }
.checker-shadow-light { fill: #737b77; }.checker-shadow-dark { fill: #303938; }
.checker-shadow-edge { fill: none; stroke: rgba(22,36,40,.3); stroke-width: 22; filter: blur(12px); transition: opacity .4s ease; }
.checker-labels { transition: opacity .25s ease; }
.checker-label { fill: white; font-size: 16px; font-weight: 900; text-anchor: middle; dominant-baseline: middle; paint-order: stroke; stroke: rgba(17,25,35,.85); stroke-width: 4; }
.checker-pointer { fill: none; stroke: var(--orange); stroke-width: 2.5; stroke-linecap: round; }
.checker-cylinder { fill: url(#cylinder-gradient); stroke: rgba(255,255,255,.45); stroke-width: 2; filter: drop-shadow(8px 12px 10px rgba(18,31,35,.32)); }
.checker-cylinder-group { transition: opacity .45s ease, transform .65s ease; transform-origin: center; }
.checker-merge { fill: #737b77; stroke: rgba(255,255,255,.22); stroke-width: 1; transition: transform .86s cubic-bezier(.22,.82,.24,1); }
.checker-merge-b { transition-delay: .18s; }
.checker-proof { opacity: 0; fill: none; stroke: var(--orange); stroke-width: 2; text-anchor: middle; font-size: 13px; transition: opacity .3s ease; }
.checker-proof text { fill: var(--ink); stroke: none; font-weight: 800; }
.checker-stage.is-revealed .checker-board { opacity: .08; transform: scale(.94); }
.checker-stage.is-revealed .checker-shadow-edge, .checker-stage.is-revealed .checker-cylinder-group, .checker-stage.is-revealed .checker-labels { opacity: 0; }
.checker-stage.is-revealed .checker-cylinder-group { transform: translateY(-24px); }
.checker-stage.is-revealed .checker-merge-a { transform: translate(90px, 48px); }
.checker-stage.is-revealed .checker-merge-b { transform: translate(-90px, -48px); }
.checker-stage.is-revealed .checker-proof { opacity: 1; transition-delay: 1.05s; }

/* 12 Drift */
.drift-stage { min-height: 540px; display: grid; place-items: center; background: radial-gradient(circle at center, #26384b, #101722 72%); }
.drift-discs { display: grid; width: min(88%, 680px); grid-template-columns: repeat(3, 1fr); gap: 12px; }
.drift-discs i { display: block; aspect-ratio: 1; border-radius: 50%; background: repeating-conic-gradient(#07111f 0deg 9deg, #4c79ff 9deg 18deg, #fff9e8 18deg 27deg, #f0a824 27deg 36deg); -webkit-mask: radial-gradient(circle, transparent 0 16%, #000 17% 32%, transparent 33% 42%, #000 43% 59%, transparent 60% 69%, #000 70% 93%, transparent 94%); mask: radial-gradient(circle, transparent 0 16%, #000 17% 32%, transparent 33% 42%, #000 43% 59%, transparent 60% 69%, #000 70% 93%, transparent 94%); }
.drift-discs i:nth-child(even) { transform: scaleX(-1); }
.drift-fixation { position: absolute; left: 50%; top: 50%; width: 13px; height: 13px; border: 3px solid white; border-radius: 50%; background: var(--orange); box-shadow: 0 0 0 5px rgba(255,92,53,.22), 0 2px 8px rgba(0,0,0,.4); transform: translate(-50%, -50%); z-index: 3; }
.drift-guide-label { position: absolute; left: 50%; bottom: 16px; color: rgba(255,255,255,.8); font-size: 11px; letter-spacing: .04em; opacity: 0; transform: translateX(-50%); transition: opacity .25s ease; }
.drift-stage.is-guiding .drift-fixation { animation: drift-gaze-guide 8s cubic-bezier(.45,0,.55,1) forwards; }
.drift-stage.is-guiding .drift-guide-label { opacity: 1; }
.drift-proof { position: absolute; inset: 18px; display: grid; place-items: end start; padding: 12px; border: 1px solid transparent; color: transparent; font-size: 11px; font-weight: 800; letter-spacing: .16em; pointer-events: none; }
.drift-stage.is-proved .drift-proof { border-color: var(--orange); color: var(--orange); }
@keyframes drift-gaze-guide {
  0%, 12% { left: 50%; top: 50%; }
  20%, 32% { left: 24%; top: 27%; }
  40%, 52% { left: 76%; top: 29%; }
  60%, 72% { left: 29%; top: 73%; }
  80%, 92% { left: 72%; top: 71%; }
  100% { left: 50%; top: 50%; }
}

/* 13 Motion aftereffect */
.motion-experiment { background: #e8e2d7; }
.motion-warning { display: flex; gap: 18px; align-items: baseline; margin: -12px 0 42px calc(28% + 36px); padding: 16px 20px; border-left: 4px solid var(--orange); background: rgba(255,92,53,.08); }
.motion-warning strong { color: var(--orange-dark); font-size: 12px; }
.motion-warning p { margin: 0; color: var(--ink-soft); font-size: 13px; }
.mae-stage { min-height: 580px; display: grid; place-items: center; }
.spiral-disc, .mae-test { width: min(86%, 520px); aspect-ratio: 1; border-radius: 50%; }
.spiral-disc { background: repeating-conic-gradient(#f6f0df 0 9deg, #101722 9deg 18deg); border: 10px solid #f6f0df; box-shadow: 0 0 0 1px rgba(255,255,255,.2); }
.mae-test { position: absolute; opacity: 0; background: repeating-radial-gradient(circle, #263543 0 2px, #d0d7d1 3px 7px); transition: opacity .18s ease; }
.mae-stage.is-adapting .spiral-disc { animation: spin 1.35s linear infinite; }
.mae-stage.is-testing .spiral-disc { opacity: 0; }
.mae-stage.is-testing .mae-test { opacity: 1; }
.mae-overlay { position: absolute; right: 20px; bottom: 18px; color: rgba(255,255,255,.58); font-size: 11px; font-weight: 800; letter-spacing: .14em; text-transform: uppercase; }
@keyframes spin { to { transform: rotate(360deg); } }
.mae-report { grid-template-columns: repeat(2, 1fr); }

/* 14 Blind spot */
.blind-stage { min-height: 390px; background: #e4e9e5; cursor: ew-resize; touch-action: pan-y; user-select: none; }
.blind-stage.is-dragging { cursor: grabbing; }
.blind-cross, .blind-dot { position: absolute; top: 50%; transform: translate(-50%,-50%); }
.blind-cross { left: 24%; font-size: 48px; font-weight: 300; line-height: 1; }
.blind-dot { left: calc(24% + var(--blind-distance, 230px)); width: 28px; height: 28px; border-radius: 50%; background: var(--orange); box-shadow: 0 0 0 8px rgba(255,92,53,.12); }
.blind-stage.is-mirrored .blind-cross { left: 76%; }
.blind-stage.is-mirrored .blind-dot { left: calc(76% - var(--blind-distance, 230px)); }
.drag-hint { position: absolute; left: 50%; bottom: 22px; transform: translateX(-50%); width: max-content; color: #59636c; font-size: 11px; letter-spacing: .04em; }

.completion { padding: 130px 7vw; color: white; background: var(--orange-dark); }
.completion .section-kicker { color: rgba(255,255,255,.94); }
.completion h2 { font-size: clamp(48px, 7vw, 100px); }
.completion h2 span { display: inline-block; color: var(--ink); }
.completion > p:not(.section-kicker) { max-width: 520px; margin: 32px 0; color: white; }

.sources { padding: 100px 7vw; display: grid; grid-template-columns: .7fr 1.3fr; gap: 7vw; color: white; background: var(--ink); }
.sources h2 { margin: 0; font-size: clamp(32px, 4vw, 56px); letter-spacing: -.045em; }
.sources > p { grid-column: 1; margin: 20px 0 0; color: rgba(255,255,255,.55); font-size: 14px; }
.sources ul { grid-column: 2; grid-row: 1 / span 2; margin: 0; padding: 0; border-top: 1px solid rgba(255,255,255,.25); list-style: none; }
.sources li { border-bottom: 1px solid rgba(255,255,255,.16); }
.sources a { display: flex; justify-content: space-between; gap: 20px; padding: 20px 0; color: rgba(255,255,255,.76); text-decoration: none; font-size: 13px; }
.sources a:hover { color: white; }
.sources a span { color: var(--orange); }
.site-footer { padding: 58px 7vw; display: grid; grid-template-columns: 1fr 1fr 1fr; align-items: end; background: #090e15; color: white; }
.footer-brand { align-self: start; }
.site-footer p { margin: 0; color: rgba(255,255,255,.5); font-size: 13px; }
.back-top { justify-self: end; color: rgba(255,255,255,.6); font-size: 12px; text-decoration: none; }

button:focus-visible, a:focus-visible, summary:focus-visible { outline: 3px solid var(--blue); outline-offset: 3px; }

@media (max-width: 980px) {
  .site-header { grid-template-columns: 1fr auto; }
  .site-nav { display: none; }
  .hero { grid-template-columns: 1fr; padding-top: 100px; }
  .hero-visual { position: absolute; right: -180px; top: 22%; width: 520px; opacity: .5; }
  .hero-copy { max-width: 760px; }
  .guide, .experiments-heading { grid-template-columns: 1fr; }
  .guide { gap: 54px; }
  .experiments-heading > p:last-child { justify-self: start; margin-top: 28px; }
  .experiment-head { grid-template-columns: 90px 1fr; }
  .experiment-intro { grid-column: 2; }
  .lab-layout, .lab-layout-flip { grid-template-columns: 1fr; }
  .lab-layout-flip .stage, .lab-layout-flip .lab-controls { grid-column: 1; }
  .lab-layout-flip .stage { grid-row: 1; }
  .lab-layout-flip .lab-controls { grid-row: 2; }
  .lab-controls { display: flex; flex-direction: column; align-items: stretch; }
  .why, .motion-warning { margin-left: 0; }
}

@media (max-width: 680px) {
  .site-header { height: 62px; padding: 0 20px; }
  .header-progress { gap: 8px; }
  .header-progress progress { width: 52px; }
  .hero { min-height: calc(100svh - 62px); padding: 76px 22px 66px; }
  .hero h1 { font-size: clamp(48px, 15vw, 70px); }
  .hero-lede { font-size: 15px; }
  .hero-actions { align-items: flex-start; flex-direction: column; }
  .hero-visual { right: -270px; opacity: .34; }
  .scroll-note { display: none; }
  .guide, .experiments-heading, .experiment, .sources, .completion { padding-left: 22px; padding-right: 22px; }
  .guide { padding-top: 72px; padding-bottom: 72px; }
  .guide-steps li { grid-template-columns: 42px 1fr; }
  .guide-steps p { grid-column: 2; }
  .comfort-note { align-items: flex-start; }
  .experiments-heading { padding-top: 90px; padding-bottom: 65px; }
  .experiment { padding-top: 70px; padding-bottom: 54px; }
  .experiment-head { grid-template-columns: 56px 1fr; gap: 18px; margin-bottom: 34px; }
  .experiment-head > div:first-child { grid-row: 1 / span 2; }
  .experiment-intro { grid-column: 2; font-size: 14px; }
  .stage, .muller-stage svg { min-height: 320px; }
  .lab-controls { display: flex; margin-top: 8px; }
  .why { margin-top: 40px; }
  .choice-group { grid-template-columns: repeat(3, 1fr); }
  .choice-group button { padding: 8px 4px; font-size: 12px; }
  .cafe-stage { min-height: 340px; }
  .cafe-grid { transform: scale(.84); width: 126%; }
  .grid-stage, .zollner-stage, .troxler-stage, .rubin-stage, .kanizsa-stage, .ponzo-stage, .checker-stage, .drift-stage, .mae-stage { min-height: 360px; }
  .trox-dot { width: 68px; height: 68px; }
  .drift-discs { width: 92%; gap: 9px; }
  .motion-warning { align-items: flex-start; }
  .sources { grid-template-columns: 1fr; }
  .sources ul { grid-column: 1; grid-row: auto; margin-top: 28px; }
  .site-footer { grid-template-columns: 1fr auto; gap: 30px; padding: 44px 22px; }
  .site-footer p { grid-column: 1 / -1; grid-row: 2; }
  .back-top { grid-column: 2; grid-row: 1; }
  .blind-dot { width: 22px; height: 22px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .mae-stage.is-adapting .spiral-disc { animation-duration: 2.7s; }
}