@charset "UTF-8";
:root {
  --ink: #102d43;
  --muted: #557081;
  --deep: #064970;
  --pool: #087eaa;
  --water: #dbf2f7;
  --white: #fff;
  --amber: #ffbe70;
  --line: #d6e5ec;
  --blue: #006b9b;
  font-family: "PingFang SC", "Noto Sans CJK SC", "Microsoft YaHei", sans-serif;
  color: var(--ink);
  background: #fff;
  font-synthesis: none;
}
* {
  box-sizing: border-box;
}
html {
  scroll-behavior: smooth;
  scroll-padding-top: 24px;
}
body {
  margin: 0;
}
button,
input,
select {
  font: inherit;
}
button,
a,
summary,
input,
select {
  -webkit-tap-highlight-color: transparent;
}
button {
  cursor: pointer;
}
a {
  color: inherit;
  text-decoration: none;
}
button {
  color: inherit;
}
button:focus-visible,
a:focus-visible,
summary:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 3px solid #de810e;
  outline-offset: 5px;
}
p {
  line-height: 1.9;
}
button:disabled {
  cursor: default;
}
main,
.site-header,
footer {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 48px;
}
.site-header {
  height: 88px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  gap: 20px;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  font-weight: 650;
  font-size: 20px;
  color: var(--deep);
  white-space: nowrap;
}
.site-header nav {
  display: flex;
  align-items: center;
  gap: 30px;
  font-size: 13px;
}
.site-header nav a:hover {
  color: var(--blue);
  text-decoration: underline;
  text-underline-offset: 6px;
}
.original {
  padding: 8px 14px;
  border: 1px solid #c5d7e1;
  border-radius: 4px;
}
.skip-link {
  position: fixed;
  top: -60px;
  left: 15px;
  z-index: 100;
  background: var(--ink);
  color: #fff;
  padding: 12px;
}
.skip-link:focus {
  top: 12px;
}
.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;
}
.opening {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 40px;
  padding: 38px 0 30px;
}
.opening-caption {
  font-size: 13px;
  color: var(--blue);
  margin: 0 0 12px;
}
.opening h1 {
  font-size: clamp(32px, 3.3vw, 46px);
  font-weight: 620;
  letter-spacing: -1.6px;
  line-height: 1.4;
  margin: 0;
}
.mobile-break {
  display: none;
}
.opening-instruction {
  font-size: 13px;
  color: var(--muted);
  margin: 0 0 3px;
}
.opening-instruction strong {
  font-weight: 500;
  color: var(--ink);
}
.observation-window {
  border-radius: 12px;
  overflow: hidden;
  background: var(--deep);
  box-shadow: 0 15px 40px -26px #06497088;
}
.water-scene {
  display: grid;
  grid-template-columns: 1.65fr 1fr;
  background:
    radial-gradient(ellipse at 25% -20%, #2ba7c8 0, transparent 65%),
    linear-gradient(170deg, #087eaa, #075378 74%);
  color: #fff;
  min-width: 0;
}
.swimmer-pane,
.foot-pane {
  position: relative;
  min-width: 0;
}
.swimmer-pane {
  padding: 20px 22px 0;
}
.foot-pane {
  padding: 20px 18px 0;
  border-left: 1px solid #c3eaff38;
  background: #032f5033;
  display: flex;
  flex-direction: column;
}
.scene-caption {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: center;
  font-size: 12px;
  position: relative;
  z-index: 1;
}
.scene-caption > span:last-child {
  font-size: 11px;
  color: #c7e8f3;
}
.scene-caption #phase-name {
  color: var(--amber);
}
canvas {
  width: 100%;
  display: block;
}
.swimmer-pane canvas {
  height: 280px;
}
.foot-pane canvas {
  height: 280px;
}
.anatomy-caption {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  padding: 0 0 22px;
  font-size: 12px;
  color: #d9eff5;
}
.anatomy-caption i {
  height: 1px;
  width: 18px;
  background: #b6e2ed77;
  position: relative;
}
.anatomy-caption i:after {
  content: "";
  position: absolute;
  right: 0;
  top: -2px;
  border-left: 4px solid #b6e2ed77;
  border-top: 2px solid transparent;
  border-bottom: 2px solid transparent;
}
.force-legend {
  display: flex;
  justify-content: center;
  gap: 15px;
  flex-wrap: wrap;
  padding: 0 0 22px;
  color: #dbf2f7;
  font-size: 11px;
}
.force-legend span {
  display: flex;
  align-items: center;
  gap: 5px;
}
.force-legend i {
  width: 16px;
  height: 3px;
  display: inline-block;
}
.force-legend .reaction {
  background: #fff;
}
.force-legend .thrust {
  background: var(--amber);
}
.force-legend .water {
  height: 0;
  border-top: 2px dashed #7de4f6;
}
.transport {
  display: flex;
  align-items: center;
  gap: 25px;
  padding: 18px 24px;
  background: #063a59;
  color: #fff;
}
.play-button {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: 0;
  background: #e9f8fc;
  color: var(--deep);
  height: 44px;
  border-radius: 6px;
  min-width: 92px;
  font-size: 13px;
}
.timeline {
  flex: 1;
  min-width: 80px;
}
.timeline > span {
  font-size: 11px;
  color: #b5dce9;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.timeline output {
  font-variant-numeric: tabular-nums;
  color: #fff;
}
.timeline input {
  display: block;
  width: 100%;
  height: 18px;
  margin: 9px 0 0;
  accent-color: #b8eaf8;
  cursor: pointer;
}
.speed-control {
  display: flex;
  align-items: center;
  gap: 9px;
  font-size: 11px;
  color: #bfdee9;
}
.speed-control select {
  background: #0b4d6d;
  color: #fff;
  border: 1px solid #6694a977;
  border-radius: 4px;
  font-size: 12px;
  height: 36px;
  padding: 0 5px;
}
.quiet-button {
  padding: 9px 8px;
  border: 0;
  background: transparent;
  font-size: 12px;
  color: inherit;
  min-height: 40px;
  white-space: nowrap;
}
.transport .quiet-button {
  color: #c3e4ee;
}
.experiment-desk {
  display: grid;
  grid-template-columns: 1.1fr 1fr;
  gap: 65px;
  padding: 30px 5px 38px;
  border-bottom: 1px solid var(--line);
}
.reading-top {
  display: flex;
  align-items: center;
  gap: 9px;
}
.live-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--blue);
  flex-shrink: 0;
}
h2,
h3 {
  font-weight: 600;
}
.reading h2 {
  font-size: 19px;
  line-height: 1.6;
  margin: 0;
}
.reading > p {
  font-size: 14px;
  margin: 12px 0;
  color: var(--muted);
  min-height: 54px;
}
.frame-buttons {
  display: flex;
  gap: 9px;
  flex-wrap: wrap;
  margin: 16px 0;
}
.frame-buttons button {
  background: #f0f7fa;
  border: 1px solid #cbdfe9;
  border-radius: 4px;
  padding: 8px 12px;
  font-size: 12px;
  min-height: 36px;
}
.frame-buttons button:hover {
  background: #deedf4;
}
.reading .model-caption {
  font-size: 11px;
  color: #6b8392;
  margin: 15px 0 0;
  min-height: 0;
  line-height: 1.8;
  max-width: 490px;
}
.angle-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.angle-heading label {
  font-size: 14px;
  font-weight: 550;
}
.angle-heading output {
  font-size: 27px;
  color: var(--blue);
  font-variant-numeric: tabular-nums;
  font-weight: 500;
}
.experiment-controls > input {
  display: block;
  width: 100%;
  height: 24px;
  accent-color: var(--blue);
  margin: 12px 0 6px;
  cursor: pointer;
}
.experiment-controls > input:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}
.range-labels {
  display: flex;
  justify-content: space-between;
  font-size: 10px;
  color: #6b8392;
}
.angle-hint {
  font-size: 12px;
  color: var(--blue);
  margin: 10px 0 15px;
  min-height: 23px;
}
.model-switch {
  display: flex;
  border: 1px solid #bad1de;
  border-radius: 5px;
  overflow: hidden;
}
.model-switch button {
  flex: 1;
  background: #fff;
  border: 0;
  border-right: 1px solid #d6e5ec;
  font-size: 12px;
  padding: 11px 7px;
  min-height: 42px;
}
.model-switch button:last-child {
  border-right: 0;
}
.model-switch button.selected {
  background: #08648e;
  color: #fff;
}
.control-bottom {
  display: flex;
  justify-content: space-between;
  gap: 15px;
  align-items: center;
  margin-top: 16px;
}
.checkbox {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 12px;
  color: var(--muted);
}
.checkbox input {
  accent-color: var(--blue);
  width: 15px;
  height: 15px;
}
.control-bottom > span {
  font-size: 10px;
  color: #718695;
}
.cycle-section {
  display: grid;
  grid-template-columns: 1fr 1.2fr;
  align-items: center;
  gap: 55px;
  padding: 32px 5px;
}
.cycle-text h2 {
  font-size: 19px;
  line-height: 1.6;
  margin: 0;
}
.cycle-text p {
  font-size: 13px;
  color: var(--muted);
  margin: 10px 0 15px;
  max-width: 440px;
}
.average {
  display: flex;
  align-items: center;
  gap: 13px;
  font-size: 12px;
}
.average > span {
  color: var(--muted);
}
.average > strong {
  color: var(--blue);
  font-size: 13px;
  font-weight: 550;
}
.cycle-chart canvas {
  height: 155px;
}
.chart-legend {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 18px;
  font-size: 10px;
  color: var(--muted);
  margin-top: 6px;
}
.chart-legend span {
  display: flex;
  align-items: center;
  gap: 5px;
}
.chart-legend i {
  width: 16px;
  height: 2px;
  background: #b66c17;
}
.chart-legend span:nth-child(2) i {
  height: 0;
  background: none;
  border-top: 1.5px dashed var(--blue);
}
.model-math {
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}
summary {
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  padding: 20px 5px;
  font-size: 12px;
  color: var(--muted);
  list-style: none;
}
summary::-webkit-details-marker {
  display: none;
}
summary > span {
  font-size: 21px;
  color: var(--blue);
  font-weight: 400;
}
details[open] summary > span {
  transform: rotate(45deg);
}
.detail-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
  background: #f0f7fa;
  padding: 25px 30px;
}
.detail-grid h3 {
  font-size: 15px;
  margin: 0 0 10px;
}
.detail-grid p {
  font-size: 12px;
  color: var(--muted);
  margin: 10px 0;
}
code {
  font-size: 12px;
  background: #e0edf3;
  color: #24465d;
  white-space: normal;
  overflow-wrap: anywhere;
  padding: 1px 3px;
}
.comparison {
  padding-top: 72px;
}
.section-intro {
  display: flex;
  justify-content: space-between;
  align-items: end;
  gap: 35px;
  margin-bottom: 25px;
}
.section-caption {
  color: var(--blue);
  font-size: 13px;
  margin: 0 0 13px;
}
.section-intro h2,
.practice-header h2,
.understand h2 {
  font-size: 36px;
  line-height: 1.4;
  letter-spacing: -1px;
  margin: 0;
}
.section-intro > p {
  font-size: 13px;
  color: var(--muted);
  margin: 0 0 4px;
}
.comparison-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  margin: 25px 0 14px;
}
.compare-picker {
  display: flex;
  gap: 18px;
}
.compare-picker button {
  border: 0;
  border-bottom: 2px solid transparent;
  background: transparent;
  font-size: 13px;
  padding: 11px 0;
  color: var(--muted);
}
.compare-picker button.selected {
  border-color: var(--blue);
  color: var(--blue);
  font-weight: 550;
}
.comparison-toolbar > .quiet-button {
  border: 1px solid var(--line);
  border-radius: 4px;
  color: var(--blue);
  padding-left: 14px;
  padding-right: 14px;
}
.comparison-pool {
  display: grid;
  grid-template-columns: 1fr 1fr;
  background: #e7f4f9;
  border-radius: 8px;
  overflow: hidden;
}
.comparison-pool figure {
  margin: 0;
  min-width: 0;
  padding: 23px 24px 10px;
}
.comparison-pool figure + figure {
  border-left: 1px solid #bdd8e5;
  background: #f0f6f8;
}
.comparison-pool figcaption {
  display: flex;
  align-items: baseline;
  gap: 12px;
  flex-wrap: wrap;
}
.comparison-pool figcaption strong {
  font-size: 16px;
  font-weight: 550;
}
.comparison-pool figcaption span {
  font-size: 11px;
  color: var(--muted);
}
.comparison-pool canvas {
  height: 200px;
}
.comparison-takeaway {
  display: grid;
  grid-template-columns: 30px 1fr 230px;
  gap: 14px;
  padding: 24px 5px;
}
.focus-symbol {
  font-size: 25px;
  color: var(--blue);
}
.comparison-takeaway h3 {
  font-size: 17px;
  margin: 4px 0 8px;
}
.comparison-takeaway p {
  font-size: 13px;
  color: var(--muted);
  margin: 0;
  max-width: 650px;
}
.comparison-takeaway .comparison-limit {
  font-size: 11px;
  border-left: 1px solid var(--line);
  padding-left: 20px;
  align-self: center;
}
.understand {
  display: grid;
  grid-template-columns: 1fr 1.4fr;
  gap: 70px;
  margin: 50px 0 72px;
  padding: 38px 0 0;
  border-top: 1px solid var(--line);
}
.understand-question > p {
  font-size: 12px;
  color: var(--muted);
}
.understand-answer > .equation {
  display: flex;
  align-items: center;
  gap: 18px;
  font-size: 20px;
  color: var(--deep);
  margin: 0 0 21px;
  flex-wrap: wrap;
}
.equation b {
  font-weight: 400;
  color: #869eac;
}
.equation strong {
  font-weight: 550;
}
.understand-answer > p {
  font-size: 14px;
  color: var(--muted);
  margin: 12px 0;
}
.practice {
  background: #e6f3f8;
  padding: 35px 40px 22px;
  border-radius: 10px;
}
.practice-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 25px;
  margin-bottom: 30px;
}
.practice-header svg {
  color: #3d95b8;
  margin-right: 25px;
}
.drill-tabs {
  display: flex;
  border-bottom: 1px solid #bad3df;
  gap: 30px;
}
.drill-tabs button {
  border: 0;
  border-bottom: 3px solid transparent;
  padding: 14px 0;
  background: transparent;
  color: #587a8b;
  font-size: 14px;
}
.drill-tabs button.selected {
  color: var(--deep);
  border-color: var(--blue);
  font-weight: 550;
}
.drill-content {
  display: grid;
  grid-template-columns: 1.5fr 1fr;
  gap: 55px;
  padding: 28px 0;
  min-height: 180px;
}
.drill-content h3 {
  font-size: 21px;
  margin: 0 0 12px;
  line-height: 1.6;
}
.drill-content p {
  font-size: 14px;
  color: var(--muted);
  margin: 0;
  max-width: 650px;
}
.drill-observe {
  border-left: 2px solid #b2d6e5;
  padding: 10px 0 10px 27px;
  align-self: center;
}
.drill-observe span {
  display: block;
  font-size: 11px;
  color: #4a7d95;
  margin-bottom: 10px;
}
.drill-observe strong {
  font-weight: 500;
  line-height: 1.8;
  font-size: 17px;
}
.practice-safety {
  border-top: 1px solid #c3dce7;
  padding-top: 16px;
  font-size: 11px;
  color: #587c8e;
  margin: 0;
}
.references {
  padding: 62px 0 38px;
  max-width: 1000px;
}
.references h2 {
  font-size: 19px;
  margin: 0 0 12px;
}
.references p {
  font-size: 12px;
  color: var(--muted);
  max-width: 800px;
}
.references > div {
  display: flex;
  gap: 12px 28px;
  flex-wrap: wrap;
  margin-top: 20px;
}
.references a {
  font-size: 11px;
  color: var(--blue);
  text-decoration: underline;
  text-underline-offset: 5px;
  line-height: 2;
}
footer {
  border-top: 1px solid var(--line);
  min-height: 100px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  font-size: 11px;
  color: var(--muted);
}
footer .brand {
  font-size: 15px;
}
footer > a:last-child {
  color: var(--blue);
  text-decoration: underline;
  text-underline-offset: 4px;
}
@media (min-width: 1500px) {
  .water-scene {
    grid-template-columns: 1.6fr 1fr;
  }
  .swimmer-pane canvas,
  .foot-pane canvas {
    height: 310px;
  }
}
@media (max-width: 1050px) {
  main,
  .site-header,
  footer {
    padding-left: 30px;
    padding-right: 30px;
  }
  .opening {
    gap: 25px;
  }
  .opening h1 {
    font-size: 34px;
  }
  .opening-instruction {
    font-size: 11px;
  }
  .water-scene {
    grid-template-columns: 1.4fr 1fr;
  }
  .scene-caption {
    font-size: 11px;
  }
  .scene-caption > span:last-child {
    font-size: 10px;
  }
  .swimmer-pane,
  .foot-pane {
    padding-left: 15px;
    padding-right: 15px;
  }
  .experiment-desk {
    gap: 35px;
  }
  .transport {
    gap: 17px;
  }
  .cycle-section {
    gap: 30px;
  }
  .comparison-pool figure {
    padding: 20px 18px 5px;
  }
  .comparison-takeaway {
    grid-template-columns: 25px 1fr 180px;
  }
  .understand {
    gap: 40px;
  }
  .understand-answer > .equation {
    font-size: 17px;
    gap: 12px;
  }
  .control-bottom {
    gap: 10px;
  }
  .control-bottom > span {
    font-size: 9px;
  }
}
@media (max-width: 760px) {
  main,
  .site-header,
  footer {
    padding-left: 20px;
    padding-right: 20px;
  }
  .site-header {
    height: 72px;
  }
  .brand {
    font-size: 17px;
    gap: 8px;
  }
  .site-header nav {
    gap: 17px;
    font-size: 11px;
  }
  .site-header .original {
    display: none;
  }
  .opening {
    padding: 28px 0 22px;
    align-items: start;
    flex-direction: column;
    gap: 13px;
  }
  .opening h1 {
    font-size: 36px;
    line-height: 1.3;
    letter-spacing: -1.5px;
  }
  .opening-caption {
    font-size: 11px;
    margin-bottom: 10px;
  }
  .opening-instruction {
    font-size: 12px;
    margin: 0;
  }
  .opening-instruction br {
    display: none;
  }
  .water-scene {
    grid-template-columns: 1fr;
  }
  .swimmer-pane {
    padding: 15px 15px 0;
    border-bottom: 1px solid #c3eaff38;
  }
  .swimmer-pane canvas {
    height: 150px;
  }
  .scene-caption {
    font-size: 12px;
  }
  .scene-caption > span:last-child {
    font-size: 11px;
  }
  .anatomy-caption {
    padding-bottom: 13px;
    font-size: 10px;
    gap: 10px;
  }
  .foot-pane {
    padding: 15px 15px 0;
    border-left: 0;
  }
  .foot-pane canvas {
    height: 255px;
  }
  .force-legend {
    padding-bottom: 17px;
    font-size: 10px;
    gap: 14px;
  }
  .transport {
    padding: 16px;
    gap: 14px;
    flex-wrap: wrap;
  }
  .play-button {
    min-width: 78px;
    height: 42px;
    font-size: 12px;
  }
  .timeline {
    flex: 1;
  }
  .timeline > span {
    font-size: 10px;
  }
  .speed-control {
    margin-left: 0;
    flex: 1;
    font-size: 11px;
    justify-content: flex-start;
    gap: 12px;
  }
  .speed-control select {
    height: 32px;
  }
  .transport .quiet-button {
    min-height: 32px;
    padding: 3px 8px;
  }
  .experiment-desk {
    grid-template-columns: 1fr;
    gap: 24px;
    padding: 25px 0 28px;
  }
  .reading h2 {
    font-size: 18px;
  }
  .reading > p {
    font-size: 13px;
    min-height: 0;
  }
  .reading .model-caption {
    font-size: 10px;
  }
  .frame-buttons button {
    font-size: 11px;
    padding: 8px 10px;
  }
  .experiment-controls {
    background: #f1f8fb;
    padding: 19px 18px;
    border-radius: 7px;
  }
  .angle-heading label {
    font-size: 13px;
  }
  .angle-heading output {
    font-size: 26px;
  }
  .range-labels {
    font-size: 9px;
  }
  .angle-hint {
    font-size: 11px;
  }
  .model-switch button {
    font-size: 11px;
    padding: 10px 4px;
  }
  .control-bottom > span {
    font-size: 9px;
  }
  .checkbox {
    font-size: 11px;
  }
  .cycle-section {
    grid-template-columns: 1fr;
    padding: 25px 0;
    gap: 15px;
  }
  .cycle-text h2 {
    font-size: 18px;
  }
  .cycle-text p {
    font-size: 12px;
    margin-bottom: 12px;
  }
  .cycle-chart canvas {
    height: 150px;
  }
  .chart-legend {
    font-size: 9px;
    gap: 12px;
  }
  .model-math summary {
    font-size: 11px;
    padding: 18px 0;
    line-height: 1.8;
  }
  .detail-grid {
    grid-template-columns: 1fr;
    padding: 22px 18px;
    gap: 20px;
  }
  .detail-grid h3 {
    font-size: 14px;
  }
  .detail-grid p {
    font-size: 12px;
  }
  .comparison {
    padding-top: 45px;
  }
  .section-intro {
    align-items: start;
    flex-direction: column;
    gap: 16px;
    margin-bottom: 16px;
  }
  .section-intro h2,
  .practice-header h2,
  .understand h2 {
    font-size: 30px;
  }
  .section-caption {
    font-size: 11px;
  }
  .section-intro > p {
    font-size: 12px;
  }
  .section-intro > p br {
    display: none;
  }
  .comparison-toolbar {
    margin-top: 10px;
  }
  .compare-picker {
    gap: 14px;
  }
  .compare-picker button {
    font-size: 12px;
  }
  .comparison-toolbar > .quiet-button {
    font-size: 11px;
    padding: 8px 10px;
    min-height: 36px;
  }
  .comparison-pool {
    grid-template-columns: 1fr;
  }
  .comparison-pool figure {
    padding: 18px 18px 0;
  }
  .comparison-pool figure + figure {
    border-left: 0;
    border-top: 1px solid #bdd8e5;
  }
  .comparison-pool canvas {
    height: 155px;
  }
  .comparison-pool figcaption strong {
    font-size: 14px;
  }
  .comparison-pool figcaption span {
    font-size: 10px;
  }
  .comparison-takeaway {
    grid-template-columns: 24px 1fr;
    padding: 21px 0;
    gap: 9px;
  }
  .comparison-takeaway h3 {
    font-size: 16px;
    line-height: 1.6;
    margin-top: 0;
  }
  .comparison-takeaway p {
    font-size: 12px;
  }
  .comparison-takeaway .comparison-limit {
    grid-column: 2;
    border: 0;
    padding: 0;
    font-size: 10px;
    margin-top: 4px;
  }
  .understand {
    grid-template-columns: 1fr;
    gap: 18px;
    margin: 25px 0 45px;
    padding-top: 30px;
  }
  .understand h2 br {
    display: none;
  }
  .understand-answer > .equation {
    font-size: 15px;
    gap: 10px;
    margin-bottom: 14px;
  }
  .understand-answer > p {
    font-size: 13px;
  }
  .understand-question > p {
    margin-bottom: 0;
  }
  .practice {
    padding: 26px 20px 20px;
    border-radius: 7px;
  }
  .practice-header {
    margin-bottom: 20px;
    gap: 10px;
  }
  .practice-header svg {
    width: 85px;
    height: 85px;
    margin-right: 0;
    flex-shrink: 0;
  }
  .drill-tabs {
    gap: 0;
    justify-content: space-between;
  }
  .drill-tabs button {
    font-size: 11px;
    padding: 12px 0;
  }
  .drill-content {
    grid-template-columns: 1fr;
    gap: 20px;
    padding: 23px 0;
    min-height: 285px;
  }
  .drill-content h3 {
    font-size: 18px;
  }
  .drill-content p {
    font-size: 12px;
  }
  .drill-observe {
    padding: 0 0 0 15px;
  }
  .drill-observe span {
    font-size: 10px;
    margin-bottom: 5px;
  }
  .drill-observe strong {
    font-size: 14px;
  }
  .practice-safety {
    font-size: 10px;
    line-height: 1.9;
  }
  .references {
    padding: 38px 0 30px;
  }
  .references h2 {
    font-size: 17px;
    line-height: 1.7;
  }
  .references p {
    font-size: 11px;
  }
  .references > div {
    display: grid;
    gap: 10px;
  }
  .references a {
    font-size: 10px;
  }
  footer {
    min-height: 120px;
    flex-wrap: wrap;
    padding-top: 22px;
    padding-bottom: 22px;
    gap: 14px;
  }
  footer > span {
    width: 100%;
    order: 3;
    font-size: 10px;
  }
}
@media (max-width: 390px) {
  main,
  .site-header,
  footer {
    padding-left: 15px;
    padding-right: 15px;
  }
  .brand {
    font-size: 15px;
  }
  .site-header nav {
    gap: 12px;
    font-size: 10px;
  }
  .opening h1 {
    font-size: 32px;
  }
  .mobile-break {
    display: block;
  }
  .opening-instruction {
    font-size: 11px;
  }
  .foot-pane {
    padding-left: 10px;
    padding-right: 10px;
  }
  .scene-caption {
    font-size: 11px;
  }
  .scene-caption > span:last-child {
    font-size: 10px;
  }
  .model-switch button {
    font-size: 10px;
  }
  .experiment-controls {
    padding: 17px 13px;
  }
  .control-bottom {
    flex-wrap: wrap;
  }
  .understand-answer > .equation {
    font-size: 14px;
    gap: 8px;
  }
  .practice {
    padding-left: 16px;
    padding-right: 16px;
  }
  .drill-tabs button {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}
@media (max-width: 760px) {
  .transport {
    display: grid;
    grid-template-columns: 80px minmax(0, 1fr);
    gap: 12px 14px;
  }
  .transport .play-button {
    grid-column: 1;
    grid-row: 1;
  }
  .timeline {
    grid-column: 2;
    grid-row: 1;
    width: 100%;
  }
  .speed-control {
    grid-column: 1 / -1;
    grid-row: 2;
    justify-self: start;
    white-space: nowrap;
  }
  .transport .quiet-button {
    grid-column: 2;
    grid-row: 2;
    justify-self: end;
  }
}