:root {
  font-family: "Segoe UI", -apple-system, BlinkMacSystemFont, sans-serif;
  color: #243b3c;
  background: #f6f7f3;
  font-synthesis: none;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  font-weight: 400;
  --accent: #287a6a;
  --muted: #6b7775;
  --border: #dce3dd;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 30px; }
body { margin: 0; }
button, input { font: inherit; }
button, a, input, summary { -webkit-tap-highlight-color: transparent; }
button { cursor: pointer; }
button:disabled { cursor: default; opacity: 0.4; }
a { color: inherit; }
button, a, input, summary, canvas { outline-offset: 5px; }
:focus-visible { outline: 3px solid #428dce; }
button { transition: background 150ms ease, border-color 150ms ease, color 150ms ease; }
[hidden] { display: none !important; }
h1, h2, h3, p { margin: 0; }
.icon { width: 20px; height: 20px; flex-shrink: 0; vertical-align: middle; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
.skip-link { position: fixed; top: -100px; left: 20px; z-index: 10; background: white; padding: 12px 20px; border-radius: 6px; }
.skip-link:focus { top: 12px; }
.site-header { height: 88px; max-width: 1480px; padding: 0 48px; margin: auto; display: flex; align-items: center; justify-content: space-between; border-bottom: 1px solid var(--border); }
.brand { text-decoration: none; display: flex; align-items: center; gap: 10px; }
.brand > .icon { width: 35px; height: 35px; color: var(--accent); }
.brand > span:first-of-type { font-size: 27px; font-weight: 650; letter-spacing: -1.2px; }
.brand-divider { height: 23px; width: 1px; background: #d2dbd5; margin: 0 10px; }
.brand small { color: var(--muted); font-size: 12px; letter-spacing: 0.1px; }
.site-header nav { display: flex; align-items: center; gap: 29px; }
.nav-link { font-size: 13px; text-decoration: none; color: #65716d; }
.nav-link:hover { color: var(--accent); }
.model-number { padding: 7px 10px; background: #e8ede6; border-radius: 5px; color: #586b60; font-family: "Consolas", monospace; font-size: 10px; letter-spacing: 1.2px; }
main { max-width: 1384px; margin: 0 auto; padding: 0 40px; }
main:focus { outline: none; }
.intro { display: flex; justify-content: space-between; align-items: center; gap: 20px; padding: 46px 0 32px; }
.eyebrow { color: var(--accent); font-size: 10px; font-weight: 650; letter-spacing: 1.9px; display: flex; align-items: center; gap: 9px; }
.little-line { height: 1px; width: 22px; background: var(--accent); }
h1 { font-size: clamp(30px, 3.1vw, 43px); font-weight: 550; line-height: 1.2; letter-spacing: -1.7px; margin-top: 12px; color: #203c3a; }
.subtitle { color: var(--muted); font-size: 14px; line-height: 1.65; margin-top: 13px; }
.topic-tag { display: flex; align-items: center; gap: 8px; flex-shrink: 0; border: 1px solid #d4dfd5; border-radius: 20px; padding: 8px 13px; font-size: 12px; color: #57705d; background: #eef2e9; }
.topic-tag .icon { width: 17px; height: 17px; }
.lab { display: grid; grid-template-columns: minmax(0, 1fr) 310px; background: #fff; border: 1px solid #d6dfd8; border-radius: 13px; overflow: hidden; box-shadow: 0 8px 25px #233e3610; }
.visual-column { min-width: 0; display: flex; flex-direction: column; }
.scene-wrap { position: relative; min-height: 510px; flex: 1; background: radial-gradient(ellipse at 48% 44%, #1c3c40 0%, #10292e 65%, #0e242a 100%); color: #e3eeea; isolation: isolate; overflow: hidden; }
.scene-heading { position: absolute; z-index: 2; inset: 26px 27px auto; display: flex; justify-content: space-between; align-items: flex-start; gap: 15px; pointer-events: none; }
.scene-eyebrow { display: flex; align-items: center; gap: 7px; font-size: 9px; letter-spacing: 1.6px; color: #9ab7b4; font-weight: 500; }
.live-dot { width: 5px; height: 5px; border-radius: 100%; background: #a7d5ad; box-shadow: 0 0 10px #98ceaa66; }
.scene-heading h2 { font-size: 15px; font-weight: 450; margin-top: 8px; letter-spacing: 0.1px; }
.camera-controls { display: flex; background: #ffffff06; border: 1px solid #ffffff14; border-radius: 6px; pointer-events: auto; }
.camera-controls button { display: grid; place-items: center; border: 0; background: none; color: #bad1ce; width: 34px; height: 34px; }
.camera-controls button:hover { background: #ffffff10; }
.camera-controls .icon { height: 17px; width: 17px; }
.scene-host { position: absolute; inset: 0; }
.scene-host canvas { display: block; width: 100%; height: 100%; cursor: grab; touch-action: none; }
.scene-host canvas:active { cursor: grabbing; }
.scene-host canvas:focus-visible { outline-offset: -4px; }
.charge-marker { position: absolute; padding: 4px 8px; border: 1px solid #f4b58a29; background: #132c30c9; border-radius: 4px; color: #f4c09c; font-family: "Consolas", monospace; font-size: 11px; white-space: nowrap; transform: translateX(-50%); pointer-events: none; }
[data-polarity="negative"] .charge-marker { color: #a4caff; border-color: #85bafa30; }
[data-polarity="neutral"] .charge-marker { color: #c3d1d0; }
.scene-status { position: absolute; top: 99px; left: 27px; padding: 5px 8px; font-size: 10px; color: #b4c9bd; border: 1px solid #addbb324; border-radius: 4px; background: #cee4d207; pointer-events: none; }
.scene-status::before { content: ''; display: inline-block; height: 4px; width: 4px; background: currentColor; border-radius: 50%; margin-right: 6px; vertical-align: middle; }
.scene-status[data-status="boundary"] { color: #f2c387; }
.scene-bottom { position: absolute; inset: auto 26px 20px; display: flex; flex-direction: column; gap: 14px; pointer-events: none; }
.legend { display: flex; gap: 17px; flex-wrap: wrap; font-size: 10px; color: #b2c6c2; }
.legend > span { display: inline-flex; align-items: center; gap: 6px; }
.legend i { width: 15px; height: 2px; display: inline-block; }
.legend-field { background: #f4b58a; }
[data-polarity="negative"] .legend-field { background: #85bafa; }
[data-polarity="neutral"] .legend-field { background: #a1b3b4; }
.legend-surface { border-top: 1px dashed #6fc9bb; }
.legend-normal { background: #d9e8d2; }
.scene-bottom > p { color: #88a5a6; font-size: 10px; display: flex; align-items: center; gap: 6px; }
.scene-bottom > p .icon { width: 14px; height: 14px; }
.graphics-error { position: absolute; top: 42%; left: 10%; right: 10%; padding: 20px; border: 1px solid #9db7b6; background: #173137; line-height: 1.7; font-size: 14px; border-radius: 7px; }
.readings { display: grid; grid-template-columns: 1fr 1fr 1.22fr; padding: 22px 25px; border-top: 1px solid #dde4df; background: #fdfefb; gap: 20px; }
.reading { display: flex; flex-direction: column; gap: 8px; min-width: 0; }
.reading + .reading { padding-left: 22px; border-left: 1px solid var(--border); }
.reading > span { color: var(--muted); font-size: 11px; display: flex; align-items: baseline; gap: 6px; }
.reading i { font-family: Georgia, serif; color: #7d8d84; }
.reading strong { font-family: "Consolas", "SFMono-Regular", monospace; font-size: clamp(15px, 1.6vw, 21px); font-weight: 400; letter-spacing: -0.7px; color: #354c42; white-space: nowrap; }
.reading-flux strong { color: #247e65; }
.controls { padding: 25px 25px 17px; border-left: 1px solid var(--border); }
.controls-intro h2 { font-size: 15px; font-weight: 600; letter-spacing: -0.2px; }
.controls-intro p { font-size: 11px; color: var(--muted); line-height: 1.6; margin-top: 5px; margin-bottom: 23px; }
.range-control { margin-top: 18px; }
.control-heading { display: flex; align-items: center; justify-content: space-between; gap: 8px; font-size: 12px; }
.control-heading label { font-weight: 550; }
.symbol { color: #859489; font-family: Georgia, serif; font-style: italic; font-size: 14px; margin-left: 5px; }
.control-heading output { font-family: "Consolas", monospace; font-size: 11px; background: #edf3ee; color: #33765e; padding: 4px 7px; border-radius: 4px; min-width: 55px; text-align: center; }
input[type="range"] { display: block; width: 100%; height: 22px; background: transparent; margin: 11px 0 0; appearance: none; cursor: pointer; --progress: 50%; }
input[type="range"]::-webkit-slider-runnable-track { height: 3px; border-radius: 10px; background: linear-gradient(to right, #6e9983 var(--progress), #e4eae4 var(--progress)); }
input[type="range"]::-webkit-slider-thumb { appearance: none; width: 14px; height: 14px; border-radius: 50%; background: #fff; border: 3px solid #52816c; margin-top: -5.5px; box-shadow: 0 1px 3px #263e4022; }
input[type="range"]::-moz-range-track { height: 3px; border-radius: 10px; background: #e4eae4; }
input[type="range"]::-moz-range-progress { height: 3px; background: #6e9983; }
input[type="range"]::-moz-range-thumb { width: 9px; height: 9px; border-radius: 50%; background: #fff; border: 3px solid #52816c; }
.range-limits { display: flex; justify-content: space-between; font-family: "Consolas", monospace; color: #64756b; font-size: 9px; margin-top: 0; }
.control-note { font-size: 10px; color: #5f7065; line-height: 1.65; margin-top: 7px; }
.control-divider { height: 1px; background: #e5eae4; margin: 18px 0; }
fieldset { border: 0; padding: 0; margin: 0; min-width: 0; }
legend { font-size: 11px; font-weight: 550; padding: 0; margin-bottom: 10px; }
.segmented { display: flex; gap: 5px; padding: 4px; background: #f1f4ef; border-radius: 6px; border: 1px solid #e6ebe4; }
.segmented label { flex: 1; position: relative; cursor: pointer; }
.segmented input { position: absolute; width: 1px; height: 1px; opacity: 0; }
.segmented span { display: flex; align-items: center; justify-content: center; gap: 7px; border: 1px solid transparent; border-radius: 4px; padding: 7px 5px; font-size: 11px; color: #63746b; }
.segmented .icon { width: 16px; height: 16px; }
.segmented input:checked + span { background: white; border-color: #d3ded3; color: #2b6c54; box-shadow: 0 1px 2px #153c1810; }
.segmented input:focus-visible + span { outline: 3px solid #428dce; outline-offset: 2px; }
.layer-controls legend { margin-bottom: 6px; }
.layer-controls label { position: relative; display: flex; align-items: center; justify-content: space-between; font-size: 11px; line-height: 1.5; padding: 6px 0; color: #5f6e65; cursor: pointer; }
.layer-controls input { position: absolute; right: 0; width: 29px; height: 17px; opacity: 0; margin: 0; }
.toggle { width: 28px; height: 16px; border-radius: 20px; background: #d9e1d9; padding: 2px; transition: background 150ms ease; }
.toggle::before { content: ''; display: block; width: 12px; height: 12px; border-radius: 50%; background: white; box-shadow: 0 1px 2px #0002; transition: transform 150ms ease; }
.layer-controls input:checked + .toggle { background: #63977b; }
.layer-controls input:checked + .toggle::before { transform: translateX(12px); }
.layer-controls input:focus-visible + .toggle { outline: 3px solid #428dce; outline-offset: 3px; }
.reset-button { width: 100%; display: flex; justify-content: center; align-items: center; gap: 7px; background: #fff; color: #627168; border: 1px solid #dce4dc; border-radius: 5px; padding: 9px; font-size: 11px; margin-top: 17px; }
.reset-button .icon { width: 14px; height: 14px; }
.reset-button:hover { background: #f0f5ef; border-color: #b7cbb9; }
.scenarios { display: flex; align-items: center; flex-wrap: wrap; gap: 9px; margin-top: 19px; }
.scenarios-label { font-size: 11px; color: #5f7060; margin-right: 7px; }
.scenario { display: inline-flex; align-items: center; gap: 8px; font-size: 11px; padding: 8px 11px; border: 1px solid #dce3d8; background: #fff9; border-radius: 6px; color: #596d60; }
.scenario:hover { background: #eaf0e7; }
.scenario[aria-pressed="true"] { background: #e9f0e5; border-color: #b3c6aa; color: #355b3e; }
.scenario-symbol { font-size: 13px; font-weight: 500; border-radius: 50%; width: 17px; height: 17px; display: inline-grid; place-items: center; }
.positive { color: #9c6648; background: #f2e5d7; }
.negative { color: #48799b; background: #e3ebf3; }
.scenario .icon { width: 15px; height: 15px; }
.insight { display: grid; grid-template-columns: 1.2fr 1fr; align-items: center; gap: 30px; padding: 25px 28px; margin-top: 25px; background: #eaf0e5; border: 1px solid #dbe4d3; border-radius: 9px; }
.insight-copy { display: flex; align-items: flex-start; gap: 15px; }
.insight-icon { border-radius: 50%; background: #dce7d4; color: #5a7c52; display: grid; place-items: center; width: 37px; height: 37px; flex-shrink: 0; }
.insight-copy h2 { font-size: 15px; font-weight: 600; color: #3a573b; margin: 0 0 7px; }
.insight-copy p { font-size: 12px; line-height: 1.85; color: #5d6f58; max-width: 540px; }
.main-equation { text-align: center; color: #3c604a; padding-left: 20px; border-left: 1px solid #cfdbc8; min-width: 0; }
.main-equation > .katex { font-size: 1.22em; }
.main-equation > span:last-child { display: block; font-size: 10px; letter-spacing: 0.2px; margin-top: 14px; color: #596d52; }
.physics-section { padding-top: 52px; padding-bottom: 32px; }
.physics-section > h2 { margin-top: 12px; font-size: 30px; font-weight: 500; letter-spacing: -1px; }
.physics-subtitle { color: var(--muted); font-size: 13px; line-height: 1.8; margin-top: 9px; }
.lesson-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 22px; margin-top: 25px; }
.lesson-card { position: relative; border-top: 1px solid #d3dfd3; padding: 24px 20px 15px 0; }
.lesson-number { font-family: "Consolas", monospace; font-size: 11px; color: #5f7459; }
.lesson-card h3 { font-size: 16px; font-weight: 550; margin-top: 12px; color: #354e3e; }
.lesson-formula { color: #537457; margin-top: 23px; margin-bottom: 19px; min-height: 34px; display: flex; align-items: center; }
.lesson-formula .katex { font-size: 1.12em; }
.lesson-card p { color: #6c786a; font-size: 12px; line-height: 1.9; max-width: 350px; }
.try-it { display: flex; align-items: center; gap: 16px; padding: 17px 20px; background: #eef1e9; border-radius: 6px; margin-top: 20px; }
.try-it > span { color: #566f4b; font-size: 9px; letter-spacing: 1.2px; font-weight: 650; flex-shrink: 0; }
.try-it p { font-size: 12px; color: #4e6348; }
.try-it .icon { margin-left: auto; width: 17px; color: #7a8f70; }
.model-notes { color: #5e6f59; font-size: 11px; margin-top: 25px; line-height: 1.8; }
.model-notes summary { cursor: pointer; width: fit-content; color: #5d7157; }
.model-notes summary .icon { width: 14px; height: 14px; margin: 0 5px; }
.model-notes p { margin-top: 12px; max-width: 920px; }
.site-footer { max-width: 1304px; margin: 0 auto; padding: 22px 0 30px; border-top: 1px solid var(--border); display: flex; justify-content: space-between; gap: 20px; color: #5f715f; font-size: 10px; }
.site-footer > span:first-child { display: flex; align-items: center; gap: 8px; }
.site-footer .icon { width: 18px; height: 18px; }
.load-error { padding: 100px 20px; text-align: center; }
.button { margin-top: 20px; padding: 10px 16px; background: #287a6a; border: 0; border-radius: 6px; color: white; }

@media (min-width: 1500px) { .scene-wrap { min-height: 560px; } }
@media (max-width: 1100px) {
  .site-header { padding: 0 28px; }
  main { padding: 0 28px; }
  .lab { grid-template-columns: minmax(0, 1fr) 285px; }
  .controls { padding: 24px 20px 17px; }
  .scene-heading { left: 20px; right: 20px; }
  .scene-heading h2 { font-size: 13px; }
  .scene-status { left: 20px; }
  .scene-bottom { left: 20px; right: 20px; }
  .readings { padding: 21px 18px; gap: 12px; }
  .reading + .reading { padding-left: 12px; }
  .reading > span { font-size: 10px; }
  .insight { gap: 20px; padding: 22px; }
  .main-equation > .katex { font-size: 1.03em; }
  .site-footer { margin-left: 28px; margin-right: 28px; }
}
@media (max-width: 850px) {
  .brand small, .brand-divider, .topic-tag { display: none; }
  .site-header { height: 74px; }
  .intro { padding-top: 32px; }
  .lab { grid-template-columns: minmax(0, 1fr); }
  .scene-wrap { height: 480px; flex: none; }
  .controls { border-left: 0; border-top: 1px solid var(--border); display: grid; grid-template-columns: 1fr 1fr; gap: 0 30px; padding: 24px; }
  .controls-intro { grid-column: 1 / -1; }
  .controls-intro p { margin-bottom: 4px; }
  .controls .control-divider { grid-column: 1 / -1; margin: 20px 0; }
  .controls .control-note { grid-column: 1 / -1; }
  .controls .shape-control { align-self: center; }
  .controls #size { margin-top: 7px; }
  .controls .shape-control + .range-control { margin-top: 0; }
  .reset-button { align-self: center; height: fit-content; }
  .reading strong { font-size: 20px; }
  .reading > span { font-size: 11px; }
  .insight { grid-template-columns: 1fr; }
  .main-equation { border-left: 0; border-top: 1px solid #cfdbc8; padding: 20px 0 0; }
  .main-equation > .katex { font-size: 1.2em; }
  .lesson-grid { gap: 18px; }
  .lesson-card h3 { font-size: 14px; }
}
@media (max-width: 560px) {
  .site-header { padding: 0 19px; }
  .brand > span:first-of-type { font-size: 24px; }
  .brand > .icon { width: 29px; height: 29px; }
  .site-header nav { gap: 15px; }
  .nav-link { font-size: 11px; }
  .model-number { display: none; }
  main { padding: 0 16px; }
  .intro { padding: 28px 2px 25px; }
  .eyebrow { font-size: 8px; letter-spacing: 1.5px; }
  h1 { font-size: 32px; letter-spacing: -1.3px; max-width: 300px; }
  .subtitle { font-size: 12px; }
  .scene-wrap { height: 420px; min-height: 420px; }
  .scene-heading { top: 20px; left: 18px; right: 15px; gap: 8px; }
  .scene-heading h2 { font-size: 12px; max-width: 180px; line-height: 1.6; }
  .scene-eyebrow { font-size: 7px; letter-spacing: 1px; }
  .camera-controls button { width: 29px; height: 29px; }
  .camera-controls .icon { width: 14px; }
  .scene-status { left: 18px; top: 83px; font-size: 9px; }
  .scene-bottom { left: 18px; right: 18px; bottom: 16px; }
  .legend { gap: 9px; font-size: 9px; }
  .scene-bottom > p { font-size: 9px; }
  .readings { gap: 8px; padding: 18px 13px; grid-template-columns: 0.85fr 0.85fr 1.3fr; }
  .reading { gap: 7px; }
  .reading + .reading { padding-left: 8px; }
  .reading > span { font-size: 9px; display: block; line-height: 1.6; }
  .reading > span i { display: none; }
  .reading strong { font-size: 13px; letter-spacing: -0.7px; }
  .controls { display: block; padding: 23px; }
  .controls .shape-control + .range-control { margin-top: 20px; }
  .controls .control-note { font-size: 11px; }
  .control-heading { font-size: 13px; }
  .layer-controls label { padding: 9px 0; font-size: 12px; }
  .reset-button { margin-top: 20px; padding: 12px; }
  .scenarios { gap: 7px; }
  .scenarios-label { flex-basis: 100%; margin: 3px 0; }
  .scenario { padding: 8px; font-size: 10px; gap: 5px; }
  .insight { padding: 20px 18px; }
  .insight-copy { gap: 10px; }
  .insight-icon { width: 28px; height: 28px; }
  .insight-icon .icon { width: 18px; }
  .insight-copy h2 { font-size: 14px; }
  .main-equation > .katex { font-size: 1.05em; }
  .physics-section { padding: 37px 4px 25px; }
  .physics-section > h2 { font-size: 27px; }
  .physics-subtitle { font-size: 12px; }
  .lesson-grid { grid-template-columns: 1fr; gap: 8px; }
  .lesson-card { padding: 20px 3px 15px; }
  .lesson-card h3 { font-size: 17px; margin-top: 9px; }
  .lesson-card p { max-width: none; }
  .lesson-formula { margin: 19px 0 14px; }
  .try-it { gap: 10px; padding: 14px; }
  .try-it p { font-size: 11px; }
  .site-footer { flex-direction: column; gap: 12px; margin: 0 20px; padding: 20px 0 25px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition: none !important; }
}