:root {
  color-scheme: light;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: #17253a;
  background: #f5f8fc;
  font-synthesis: none;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  min-width: 320px;
  background:
    radial-gradient(circle at 88% 2%, rgba(26, 95, 208, .11), transparent 28rem),
    linear-gradient(#fbfdff, #f5f8fc 28rem);
  line-height: 1.65;
}

a { color: inherit; }

main {
  width: min(1180px, calc(100% - 40px));
  margin-inline: auto;
}

.topic-site-header {
  width: min(1160px, calc(100% - 40px));
  min-height: 78px;
  margin-inline: auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid #d7e0eb;
}

.topic-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: #17243a;
  font-size: 1.08rem;
  font-weight: 800;
  letter-spacing: -.02em;
  text-decoration: none;
}

.topic-brand img { border-radius: 10px; }
.topic-brand > span > span { color: #1a5fd0; }

.topic-site-header nav,
.topic-footer nav {
  display: flex;
  align-items: center;
}

.topic-site-header nav { gap: 6px; }
.topic-footer nav { gap: 20px; }

.topic-site-header nav > a,
.topic-footer a {
  color: #52647b;
  font-weight: 650;
  text-decoration: none;
}

.topic-site-header nav > a {
  padding: 9px 12px;
  border-radius: 9px;
  font-size: .9rem;
}

.topic-site-header nav > a:not(.button-link):hover,
.topic-site-header nav > a:not(.button-link):focus-visible,
.topic-site-header nav > a[aria-current="page"] {
  background: #e6eefb;
  color: #12489f;
}

.topic-footer a:hover,
.topic-footer a:focus-visible,
.text-link:hover {
  color: #12489f;
  text-decoration: underline;
  text-underline-offset: 4px;
}

.topic-site-header nav > .button-link.compact {
  min-height: 0;
  margin-left: 5px;
  padding: 9px 12px;
  border: 0;
  background: #1a5fd0;
  color: #fff;
  box-shadow: none;
}

.topic-site-header nav > .button-link.compact:hover,
.topic-site-header nav > .button-link.compact:focus-visible {
  background: #12489f;
  color: #fff;
}

main { padding-block: 32px 72px; }

.breadcrumbs {
  display: flex;
  gap: 9px;
  align-items: center;
  margin: 2px 0 22px;
  color: #63748d;
  font-size: .9rem;
}

.breadcrumbs a { font-weight: 700; text-decoration: none; }

.topic-hero {
  position: relative;
  overflow: hidden;
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(320px, .65fr);
  gap: clamp(34px, 6vw, 80px);
  align-items: center;
  padding: clamp(36px, 7vw, 76px);
  border: 1px solid #d9e4f1;
  border-radius: 32px;
  background: rgba(255, 255, 255, .92);
  box-shadow: 0 24px 70px rgba(44, 72, 110, .11);
}

.topic-hero::after {
  content: "";
  position: absolute;
  width: 360px;
  height: 360px;
  right: -160px;
  top: -190px;
  border-radius: 50%;
  background: rgba(26, 95, 208, .1);
  pointer-events: none;
}

.topic-library-hero { min-height: 500px; }

.hero-copy { position: relative; z-index: 1; }

.eyebrow {
  margin: 0 0 8px;
  color: #1762c3;
  font-size: .78rem;
  font-weight: 800;
  letter-spacing: .12em;
  text-transform: uppercase;
}

h1,
h2,
p { margin-top: 0; }

h1,
h2 {
  color: #12233a;
  line-height: 1.12;
  letter-spacing: -.035em;
}

h1 {
  max-width: 780px;
  margin-bottom: 19px;
  font-size: clamp(2.35rem, 5.7vw, 4.9rem);
}

.hero-copy > p:not(.eyebrow) {
  max-width: 700px;
  margin-bottom: 28px;
  color: #4c607b;
  font-size: clamp(1.05rem, 1.8vw, 1.25rem);
}

.hero-copy > small { display: block; margin-top: 16px; color: #65758c; }

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.button-link {
  display: inline-flex;
  min-height: 48px;
  align-items: center;
  justify-content: center;
  padding: 11px 19px;
  border: 1px solid #1a5fd0;
  border-radius: 12px;
  background: #1a5fd0;
  color: white;
  font-weight: 800;
  text-decoration: none;
  box-shadow: 0 8px 20px rgba(26, 95, 208, .19);
}

.button-link:hover { background: #124fae; }

.button-link.secondary {
  background: white;
  color: #1859b8;
  box-shadow: none;
}

.button-link.secondary:hover { background: #f0f6ff; }

.button-link.compact {
  min-height: 38px;
  padding: 7px 13px;
  border-radius: 9px;
  font-size: .88rem;
}

.equation-card,
.hero-model {
  position: relative;
  z-index: 1;
  border: 1px solid #cdddf1;
  border-radius: 24px;
  background: linear-gradient(145deg, #edf5ff, #fff);
  box-shadow: 0 18px 46px rgba(29, 77, 141, .12);
}

.topic-hero-side {
  position: relative;
  z-index: 1;
  display: grid;
  gap: 16px;
  min-width: 0;
}

.lesson-hero-visual {
  position: relative;
  display: block;
  overflow: hidden;
  min-height: 210px;
  border: 1px solid #cdddf1;
  border-radius: 24px;
  background:
    radial-gradient(circle at 82% 15%, rgba(36, 114, 218, .16), transparent 40%),
    linear-gradient(145deg, #edf6ff, #fff 62%, #eaf3ff);
  box-shadow: 0 18px 46px rgba(29, 77, 141, .12);
}

.lesson-hero-visual svg,
.lesson-hero-visual img {
  display: block;
  width: 100%;
  height: 210px;
  object-fit: cover;
}

.lesson-launch-preview {
  color: inherit;
  text-decoration: none;
  transition: border-color .2s ease, box-shadow .2s ease, transform .2s ease;
}

.lesson-launch-preview::after {
  content: "";
  position: absolute;
  inset: 0;
  background: rgba(17, 39, 67, 0);
  transition: background .2s ease;
}

.lesson-launch-preview:hover,
.lesson-launch-preview:focus-visible {
  border-color: #5795df;
  box-shadow: 0 18px 38px rgba(29, 78, 139, .2);
  transform: translateY(-2px);
}

.lesson-launch-preview:hover::after,
.lesson-launch-preview:focus-visible::after { background: rgba(17, 39, 67, .08); }

.lesson-play-button {
  position: absolute;
  z-index: 2;
  left: 50%;
  top: 50%;
  width: 76px;
  height: 76px;
  display: grid;
  place-items: center;
  border: 4px solid rgba(255, 255, 255, .94);
  border-radius: 50%;
  background: rgba(20, 32, 49, .72);
  box-shadow: 0 9px 25px rgba(12, 30, 54, .28);
  transform: translate(-50%, -58%);
  transition: background .2s ease, transform .2s ease;
}

.lesson-play-button span {
  width: 0;
  height: 0;
  margin-left: 6px;
  border-top: 15px solid transparent;
  border-bottom: 15px solid transparent;
  border-left: 25px solid white;
}

.lesson-launch-preview:hover .lesson-play-button,
.lesson-launch-preview:focus-visible .lesson-play-button {
  background: rgba(16, 91, 185, .9);
  transform: translate(-50%, -58%) scale(1.06);
}

.lesson-launch-preview > strong {
  position: absolute;
  z-index: 2;
  left: 50%;
  bottom: 14px;
  padding: 5px 11px;
  border-radius: 999px;
  background: rgba(255, 255, 255, .9);
  color: #174f95;
  font-size: .76rem;
  white-space: nowrap;
  transform: translateX(-50%);
}

.equation-card { padding: 28px; }
.equation-card > p { margin-bottom: 2px; color: #54708f; font-size: .76rem; font-weight: 800; letter-spacing: .09em; text-transform: uppercase; }
.equation-card h2 { margin-bottom: 19px; font-size: 1.35rem; }
.equation-card ul { display: grid; gap: 10px; margin: 0; padding: 0; list-style: none; }
.equation-card li span {
  display: block;
  padding: 12px 14px;
  border: 1px solid #d7e4f3;
  border-radius: 10px;
  background: white;
  color: #143c75;
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1.08rem;
  font-weight: 700;
  text-align: center;
}

.hero-model {
  min-height: 270px;
  overflow: hidden;
  background:
    linear-gradient(rgba(26, 95, 208, .08) 1px, transparent 1px),
    linear-gradient(90deg, rgba(26, 95, 208, .08) 1px, transparent 1px),
    linear-gradient(145deg, #eef6ff, #fff);
  background-size: 32px 32px, 32px 32px, auto;
}

.model-axis { position: absolute; left: 10%; right: 8%; bottom: 24%; height: 4px; border-radius: 2px; background: #9db5d2; }
.model-block { position: absolute; width: 80px; height: 62px; left: 29%; bottom: calc(24% + 4px); border: 4px solid #1258b8; border-radius: 10px; background: #5e9ef2; box-shadow: 0 8px 14px rgba(16, 60, 120, .2); }
.model-vector { position: absolute; width: 125px; height: 5px; left: calc(29% + 48px); bottom: calc(24% + 98px); border-radius: 3px; background: #e49c14; transform: rotate(-10deg); transform-origin: left center; }
.model-vector::after { content: ""; position: absolute; right: -3px; top: -7px; border-left: 15px solid #e49c14; border-top: 9px solid transparent; border-bottom: 9px solid transparent; }
.model-label { position: absolute; left: calc(29% + 115px); bottom: calc(24% + 111px); color: #a96700; font-family: Georgia, serif; font-size: 1.35rem; font-style: italic; font-weight: 800; }

.topic-content-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 340px;
  gap: clamp(28px, 5vw, 68px);
  align-items: start;
  padding: clamp(52px, 8vw, 88px) clamp(4px, 3vw, 34px);
}

.topic-article { display: grid; gap: 58px; min-width: 0; }
.atwood-table-wrap, .lab-table-wrap { max-width: 100%; overflow-x: auto; margin: 24px 0; }
.atwood-table, .lab-table { width: 100%; border-collapse: collapse; font-variant-numeric: tabular-nums; font-size: .92rem; }
.atwood-table caption, .lab-table caption { text-align: left; color: #415570; margin-bottom: 14px; line-height: 1.6; }
.atwood-table th, .atwood-table td, .lab-table th, .lab-table td { padding: 12px 10px; text-align: right; border-bottom: 1px solid #d1dce9; }
.atwood-table th, .lab-table th { background: #eaf1fa; color: #122d50; }
.atwood-table tbody tr:nth-child(even), .lab-table tbody tr:nth-child(even) { background: #f5f8fc; }
.atwood-calculation, .lab-calculation { padding: 16px 20px; border-left: 3px solid #1a5fd0; background: #eaf1fa; overflow-wrap: anywhere; }
.math-vector { position: relative; display: inline-block; padding-top: .08em; line-height: .9; }
.math-vector::before { content: ""; position: absolute; left: .02em; right: -.08em; top: -.02em; border-top: .08em solid currentColor; }
.math-vector::after { content: ""; position: absolute; right: -.1em; top: -.09em; width: 0; height: 0; border-top: .13em solid transparent; border-bottom: .13em solid transparent; border-left: .22em solid currentColor; }
#lab-downloads { scroll-margin-top: 100px; }
.topic-article section { max-width: 760px; }
.topic-article h2,
.learning-panel h2,
.related-topics h2,
.topic-callout h2 { margin-bottom: 18px; font-size: clamp(1.7rem, 3vw, 2.35rem); }
.topic-article p:not(.eyebrow) { color: #415570; font-size: 1.04rem; }

.investigation-list {
  display: grid;
  gap: 12px;
  margin: 25px 0 0;
  padding: 0;
  counter-reset: investigation;
  list-style: none;
}

.investigation-list li {
  position: relative;
  min-height: 54px;
  padding: 14px 16px 14px 58px;
  border: 1px solid #dae4ef;
  border-radius: 13px;
  background: white;
  color: #354a66;
}

.investigation-list li::before {
  counter-increment: investigation;
  content: counter(investigation);
  position: absolute;
  left: 15px;
  top: 11px;
  width: 32px;
  height: 32px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: #e7f1ff;
  color: #1358b8;
  font-weight: 850;
}

.misconception {
  padding: 27px;
  border: 1px solid #ebd69f;
  border-radius: 18px;
  background: #fffaf0;
}

.misconception h2 { font-size: 1.45rem; }
.misconception p:last-child { margin-bottom: 0; }

.learning-panel {
  position: sticky;
  top: 24px;
  padding: 28px;
  border: 1px solid #d5e1ef;
  border-radius: 20px;
  background: white;
  box-shadow: 0 18px 46px rgba(38, 64, 97, .09);
}

.learning-panel h2 { font-size: 1.55rem; }
.learning-panel ul { display: grid; gap: 13px; margin: 0; padding-left: 22px; color: #40546e; }
.learning-panel li::marker { color: #1a5fd0; font-weight: 800; }

.learning-action {
  display: grid;
  gap: 8px;
  margin-top: 26px;
  padding-top: 22px;
  border-top: 1px solid #e1e8f1;
}

.learning-action span { color: #5d6e83; font-size: .92rem; }

.text-link {
  color: #175dbf;
  font-weight: 800;
  text-decoration: none;
}

.related-topics,
.topic-callout {
  padding: clamp(30px, 5vw, 52px);
  border-radius: 25px;
}

.related-topics { border: 1px solid #d7e2ee; background: white; }
.related-topics > div { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; }
.related-topics > div > a { display: grid; gap: 5px; padding: 18px; border: 1px solid #dce6f2; border-radius: 14px; background: #f8fbff; text-decoration: none; }
.related-topics > div > a:hover { border-color: #83abe2; background: #f0f6ff; }
.related-topics span { color: #63768e; font-size: .75rem; font-weight: 800; letter-spacing: .08em; text-transform: uppercase; }
.related-topics strong { color: #15385f; }

.topic-list { display: grid; gap: 66px; padding-block: 76px 10px; }
.section-heading { margin-bottom: 20px; }
.section-heading p { margin-bottom: 3px; color: #1a5fd0; font-size: .82rem; font-weight: 850; letter-spacing: .1em; text-transform: uppercase; }
.section-heading h2 { margin-bottom: 0; font-size: clamp(1.8rem, 3vw, 2.5rem); }
.topic-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }

.topic-card {
  display: flex;
  min-height: 410px;
  flex-direction: column;
  overflow: hidden;
  border: 1px solid #d9e4ef;
  border-radius: 22px;
  background: white;
  box-shadow: 0 12px 32px rgba(48, 71, 100, .07);
  transition: border-color .2s ease, box-shadow .2s ease, transform .2s ease;
}

.topic-card:hover {
  border-color: #a8c4e8;
  box-shadow: 0 20px 46px rgba(39, 75, 119, .13);
  transform: translateY(-4px);
}

.topic-card-visual {
  display: block;
  min-height: 154px;
  overflow: hidden;
  border-bottom: 1px solid #dbe7f3;
  background:
    radial-gradient(circle at 84% 12%, rgba(36, 114, 218, .16), transparent 38%),
    linear-gradient(145deg, #edf6ff, #f9fcff 58%, #eaf3ff);
}

.topic-card-visual svg,
.topic-card-visual img {
  display: block;
  width: 100%;
  height: 154px;
  object-fit: cover;
  transition: transform .25s ease;
}

.topic-card:hover .topic-card-visual svg,
.topic-card:hover .topic-card-visual img { transform: scale(1.025); }

.diagram-grid,
.diagram-muted,
.diagram-path,
.diagram-surface,
.diagram-right-angle,
.diagram-force,
.diagram-accent,
.diagram-spring {
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.diagram-grid { stroke: #d8e6f6; stroke-width: 1; }
.diagram-muted { stroke: #91a8c3; stroke-width: 4; }
.diagram-path { stroke: #4d80bf; stroke-width: 4; stroke-dasharray: 8 7; }
.diagram-surface { stroke: #55708e; stroke-width: 5; }
.diagram-right-angle { fill: none; stroke: #55708e; stroke-width: 3; }
.diagram-force { stroke: #1765ca; stroke-width: 5; }
.diagram-accent { stroke: #e39a18; stroke-width: 5; }
.diagram-spring { stroke: #1765ca; stroke-width: 4; }
.diagram-object { fill: #5f9ff0; stroke: #155ebd; stroke-width: 4; }
.diagram-object-alt { fill: #f0b64e; stroke: #b97600; }
.diagram-wheel { fill: white; stroke: #155ebd; stroke-width: 5; }
.diagram-label { fill: #173a65; font-family: Georgia, "Times New Roman", serif; font-size: 15px; font-style: italic; font-weight: 700; }

.preview-grid,
.preview-axis,
.preview-ticks,
.preview-surface,
.preview-rope,
.preview-path,
.preview-vector,
.preview-vector-accent,
.preview-rough,
.preview-angle,
.preview-wall,
.preview-spring,
.preview-ceiling,
.preview-beam,
.preview-measure,
.preview-reference,
.preview-spoke,
.preview-rotation {
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.preview-grid { stroke: #dbe7f4; stroke-width: 1; }
.preview-axis { stroke: #526b8a; stroke-width: 4; }
.preview-ticks { stroke: #8fa3ba; stroke-width: 2; }
.preview-surface,
.preview-wall,
.preview-ceiling,
.preview-beam { stroke: #516c8a; stroke-width: 5; }
.preview-rope { stroke: #667f9d; stroke-width: 3; }
.preview-path { stroke: #6790c3; stroke-width: 3; stroke-dasharray: 7 6; }
.preview-vector { stroke: #036d91; stroke-width: 4; }
.preview-vector-accent { stroke: #e49b14; stroke-width: 4; }
.preview-rough { stroke: #788ea7; stroke-width: 2; }
.preview-angle,
.preview-measure,
.preview-reference { stroke: #8aa3c0; stroke-width: 2; }
.preview-spring { stroke: #1765ca; stroke-width: 3.5; }
.preview-spoke { stroke: #315f91; stroke-width: 3; }
.preview-rotation { stroke: #e49b14; stroke-width: 3; }

.preview-block,
.preview-alt-block,
.preview-cabin,
.preview-target {
  stroke-width: 2.5;
}

.preview-block { fill: #56d2e9; fill-opacity: .88; stroke: #17628b; }
.preview-alt-block { fill: #f3bd54; fill-opacity: .9; stroke: #a96f08; }
.preview-disk { fill: #55d0e9; stroke: #17628b; stroke-width: 2.5; }
.preview-alt { fill: #f3bd54; stroke: #a96f08; stroke-width: 2.5; }
.preview-hoop { fill: rgba(85, 208, 233, .14); stroke: #17628b; stroke-width: 5; }
.preview-center { fill: #173c68; }
.preview-person { fill: #f3bd54; stroke: #a96f08; stroke-width: 2; }
.preview-cabin { fill: rgba(255, 255, 255, .38); stroke: #68819d; }
.preview-target { fill: rgba(74, 158, 240, .15); stroke: #1765ca; }
.preview-target-dot { fill: #e49b14; stroke: #9b6505; stroke-width: 2; }
.preview-pulley { fill: white; stroke: #1765ca; stroke-width: 4; }
.preview-heavy-pulley { fill: #dbeaff; stroke: #1765ca; stroke-width: 5; }
.preview-planet { fill: #f3bd54; stroke: #a96f08; stroke-width: 3; }
.preview-rotor { fill: rgba(85, 208, 233, .2); stroke: #17628b; stroke-width: 5; }
.preview-pivot { fill: #f3bd54; stroke: #a96f08; stroke-width: 2; }
.preview-treasure { fill: #f3bd54; stroke: #a96f08; stroke-width: 2; }

.preview-label,
.preview-value,
.preview-accent-label {
  font-family: Inter, ui-sans-serif, system-ui, sans-serif;
  font-size: 11px;
}

.preview-label { fill: #1b2f4b; font-weight: 650; }
.preview-value { fill: #026d91; font-weight: 800; }
.preview-accent-label { fill: #b47300; font-weight: 800; }

.topic-card-body {
  display: flex;
  flex: 1;
  flex-direction: column;
  padding: 23px 24px 25px;
}

.topic-card-body > p { margin-bottom: 10px; color: #5a7090; font-size: .76rem; font-weight: 800; letter-spacing: .07em; text-transform: uppercase; }
.topic-card h2 { margin-bottom: 12px; font-size: 1.42rem; }
.topic-card h2 a { text-decoration: none; }
.topic-card-body > span { margin-bottom: 20px; color: #53667f; }
.topic-card .text-link { margin-top: auto; }

.experiment-card { min-height: 480px; }

.experiment-card-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  margin-top: auto;
}

.experiment-card-actions > a:last-child {
  color: #5c7089;
  font-size: .85rem;
  font-weight: 750;
  text-decoration: none;
}

.experiment-card-actions > a:last-child:hover { color: #1458ba; }

.resource-badges {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  margin: 0 0 18px;
}

.resource-badges span {
  padding: 3px 8px;
  border: 1px solid #cbdcf0;
  border-radius: 999px;
  background: #f1f7ff;
  color: #2a5f9f;
  font-size: .67rem;
  font-weight: 850;
  letter-spacing: .08em;
}

.experiment-library-hero .experiment-hero-visual,
.experiment-detail-hero .experiment-hero-visual {
  position: relative;
  z-index: 1;
  overflow: hidden;
  min-height: 250px;
  border: 1px solid #d4e2f2;
  border-radius: 24px;
  background:
    radial-gradient(circle at 82% 15%, rgba(36, 114, 218, .16), transparent 40%),
    linear-gradient(145deg, #edf6ff, #fff 62%, #eaf3ff);
}

.experiment-hero-visual svg,
.experiment-hero-visual img { display: block; width: 100%; height: 250px; object-fit: cover; }

.experiment-launch-preview {
  color: inherit;
  text-decoration: none;
  transition: border-color .2s ease, box-shadow .2s ease, transform .2s ease;
}

.experiment-launch-preview::after {
  content: "";
  position: absolute;
  inset: 0;
  background: rgba(17, 39, 67, 0);
  transition: background .2s ease;
}

.experiment-launch-preview:hover,
.experiment-launch-preview:focus-visible {
  border-color: #5795df;
  box-shadow: 0 18px 38px rgba(29, 78, 139, .2);
  transform: translateY(-2px);
}

.experiment-launch-preview:hover::after,
.experiment-launch-preview:focus-visible::after { background: rgba(17, 39, 67, .08); }

.experiment-play-button {
  position: absolute;
  z-index: 2;
  left: 50%;
  top: 50%;
  width: 82px;
  height: 82px;
  display: grid;
  place-items: center;
  border: 4px solid rgba(255, 255, 255, .94);
  border-radius: 50%;
  background: rgba(20, 32, 49, .72);
  box-shadow: 0 9px 25px rgba(12, 30, 54, .28);
  transform: translate(-50%, -58%);
  transition: background .2s ease, transform .2s ease;
}

.experiment-play-button span {
  width: 0;
  height: 0;
  margin-left: 7px;
  border-top: 17px solid transparent;
  border-bottom: 17px solid transparent;
  border-left: 27px solid white;
}

.experiment-launch-preview:hover .experiment-play-button,
.experiment-launch-preview:focus-visible .experiment-play-button {
  background: rgba(16, 91, 185, .9);
  transform: translate(-50%, -58%) scale(1.06);
}

.experiment-launch-preview > strong {
  position: absolute;
  z-index: 2;
  left: 50%;
  bottom: 17px;
  padding: 5px 11px;
  border-radius: 999px;
  background: rgba(255, 255, 255, .9);
  color: #174f95;
  font-size: .76rem;
  transform: translateX(-50%);
}

.experiment-question {
  margin-top: 28px;
  padding: clamp(26px, 5vw, 42px);
  border: 1px solid #cfe0f4;
  border-radius: 22px;
  background: linear-gradient(135deg, #eaf4ff, #f8fbff);
}

.experiment-introduction,
.experiment-benefits {
  margin-top: 28px;
  padding: clamp(26px, 5vw, 42px);
  border: 1px solid #d7e2ee;
  border-radius: 22px;
  background: #fff;
}

.experiment-introduction h2,
.experiment-benefits h2 {
  margin: 0 0 14px;
  font-size: clamp(1.55rem, 3vw, 2.2rem);
}

.experiment-introduction p:last-child {
  max-width: 920px;
  margin-bottom: 0;
  color: #415570;
  font-size: 1.04rem;
}

.experiment-video {
  margin-top: 28px;
  padding: clamp(26px, 5vw, 42px);
  border: 1px solid #d7e2ee;
  border-radius: 22px;
  background: #fff;
}

.experiment-video h2 {
  margin: 0 0 14px;
  font-size: clamp(1.55rem, 3vw, 2.2rem);
}

.experiment-video > p:not(.eyebrow):not(.experiment-video-link) {
  max-width: 820px;
  color: #415570;
  font-size: 1.04rem;
}

.experiment-video-frame {
  width: min(100%, 1000px);
  margin-top: 24px;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  border: 1px solid #c8d9ec;
  border-radius: 18px;
  background: #0f2037;
  box-shadow: 0 18px 42px rgba(23, 65, 116, .16);
}

.experiment-video-frame iframe {
  display: block;
  width: 100%;
  height: 100%;
  border: 0;
}

.experiment-video-link { margin: 18px 0 0; }

.experiment-benefits {
  display: grid;
  grid-template-columns: minmax(0, .8fr) minmax(0, 1.2fr);
  gap: clamp(24px, 5vw, 58px);
  align-items: start;
}

.experiment-benefits ul {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.experiment-benefits li {
  position: relative;
  padding: 13px 14px 13px 38px;
  border: 1px solid #dce6f2;
  border-radius: 13px;
  background: #f8fbff;
  color: #29425f;
}

.experiment-benefits li::before {
  position: absolute;
  top: 12px;
  left: 14px;
  color: #1a5fd0;
  content: '✓';
  font-weight: 800;
}

.experiment-question h2 {
  max-width: 900px;
  margin: 0;
  font-size: clamp(1.55rem, 3vw, 2.35rem);
}

.variable-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.variable-grid > div {
  padding: 22px;
  border: 1px solid #dbe5f0;
  border-radius: 15px;
  background: #f9fbfe;
}

.variable-grid h3 { margin: 0 0 13px; color: #173b65; font-size: 1.05rem; }
.variable-grid ul { display: grid; gap: 8px; margin: 0; padding-left: 20px; color: #465b75; }

.experiment-equations {
  list-style: none;
  margin: 0 !important;
  padding: 0 !important;
}

.experiment-equations li {
  display: grid;
  min-height: 52px;
  place-items: center;
  padding: 10px;
  border: 1px solid #d7e3f1;
  border-radius: 12px;
  background: #f9fbfe;
  color: #153f77;
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1.08rem;
  font-weight: 700;
  text-align: center;
}

.experiment-equations sub { font-size: 70%; line-height: 0; vertical-align: sub; }
.experiment-learning-panel .resource-badges { margin-top: 12px; margin-bottom: 0; }
.experiment-related { margin-top: 20px; }

.topic-callout {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 28px;
  margin-top: 64px;
  background: #122d50;
  color: #dbe9f9;
}

.topic-callout h2 { margin-bottom: 10px; color: white; }
.topic-callout p:last-child { max-width: 680px; margin-bottom: 0; }

.topic-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: min(1080px, calc(100% - 40px));
  margin: 0 auto;
  padding: 26px 0 38px;
  border-top: 1px solid #d1dce9;
  color: #64758b;
  font-size: .84rem;
}

.topic-footer p { margin: 0; }

@media (max-width: 900px) {
  .topic-hero { grid-template-columns: 1fr; }
  .topic-library-hero { min-height: auto; }
  .hero-model { min-height: 220px; }
  .topic-content-grid { grid-template-columns: 1fr; }
  .learning-panel { position: static; }
  .topic-grid { grid-template-columns: repeat(2, 1fr); }
  .related-topics > div { grid-template-columns: 1fr; }
}

@media (max-width: 820px) {
  .topic-site-header { min-height: 70px; }
  .topic-site-header nav > a:not(.button-link) { display: none; }
}

@media (max-width: 640px) {
  .topic-site-header { width: min(100% - 28px, 1160px); }
  main { width: min(100% - 24px, 1180px); }
  .topic-footer { width: min(100% - 28px, 1080px); }
  .topic-site-header { min-height: 72px; }
  .topic-brand img { width: 34px; height: 34px; }
  .topic-site-header nav > .button-link.compact { padding: 8px 10px; font-size: .82rem; }
  main { padding-top: 20px; }
  .topic-hero { padding: 28px 22px; border-radius: 22px; }
  h1 { font-size: clamp(2.15rem, 12vw, 3.25rem); }
  .hero-actions { display: grid; }
  .button-link { width: 100%; }
  .button-link.compact { width: auto; }
  .topic-content-grid { padding-block: 48px; }
  .topic-grid { grid-template-columns: 1fr; }
  .topic-card { min-height: auto; }
  .experiment-card-actions { align-items: flex-start; flex-direction: column; }
  .variable-grid { grid-template-columns: 1fr; }
  .experiment-benefits { grid-template-columns: 1fr; }
  .experiment-benefits ul { grid-template-columns: 1fr; }
  .experiment-library-hero .experiment-hero-visual,
  .experiment-detail-hero .experiment-hero-visual { min-height: 190px; }
  .experiment-hero-visual svg,
  .experiment-hero-visual img { height: 190px; }
  .experiment-play-button { width: 68px; height: 68px; }
  .experiment-play-button span { border-top-width: 14px; border-bottom-width: 14px; border-left-width: 23px; }
  .lesson-hero-visual { min-height: 190px; }
  .lesson-hero-visual svg,
  .lesson-hero-visual img { height: 190px; }
  .lesson-play-button { width: 66px; height: 66px; }
  .lesson-play-button span { border-top-width: 13px; border-bottom-width: 13px; border-left-width: 22px; }
  .topic-callout,
  .topic-footer { align-items: flex-start; flex-direction: column; }
  .topic-footer nav { flex-wrap: wrap; gap: 12px 20px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .topic-card,
  .topic-card-visual svg,
  .topic-card-visual img { transition: none; }
}