:root {
  font:
    13px system-ui,
    -apple-system,
    BlinkMacSystemFont,
    "Segoe UI",
    sans-serif;
  color: #354438;
  background: #f2f0e9;
  --line: #ccd3c7;
  --ink: #354438;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  overflow: hidden;
}
button,
input {
  font: inherit;
  color: inherit;
}
button {
  cursor: pointer;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #fffefa;
  padding: 8px 12px;
}
button:hover {
  background: #eaf0e6;
}
button:focus-visible,
input:focus-visible,
canvas:focus-visible {
  outline: 2px solid #63876a;
  outline-offset: 3px;
}
header {
  height: 62px;
  display: flex;
  align-items: center;
  padding: 0 24px;
  gap: 20px;
  border-bottom: 1px solid var(--line);
  background: #fbfaf5;
}
.brand {
  display: flex;
  align-items: center;
  gap: 11px;
  text-decoration: none;
  color: var(--ink);
  font-weight: 600;
  font-size: 16px;
  white-space: nowrap;
}
.brand > span {
  font: italic 30px Georgia;
  color: #6d8871;
}
.subtitle {
  font-size: 11px;
  color: #929c8c;
}
.playback {
  margin-left: auto;
  display: flex;
  gap: 8px;
}
.playback button {
  font-size: 11px;
}
#pause {
  min-width: 80px;
  background: #435d49;
  color: white;
  border-color: #435d49;
}
main {
  height: calc(100dvh - 62px);
  position: relative;
}
canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
}
.tools {
  position: absolute;
  top: 20px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 9px;
  background: #fffef9f2;
  border: 1px solid #d2d6ca;
  border-radius: 13px;
  box-shadow: 0 8px 30px #3b4b3610;
  white-space: nowrap;
}
.tools button {
  display: flex;
  align-items: center;
  gap: 7px;
  border-color: transparent;
  background: transparent;
  font-size: 11px;
}
.tools b {
  font-size: 23px;
  line-height: 1;
  font-weight: 400;
  color: #82957e;
}
.tools .active {
  background: #e5eedf;
  border-color: #b6c9ad;
}
.tools .active b {
  color: #4f7547;
}
.divider {
  height: 25px;
  border-left: 1px solid #dde2d6;
  margin: 0 3px;
}
.vectors {
  font-size: 10px;
  display: flex;
  gap: 6px;
  align-items: center;
  padding: 0 8px;
}
input[type="checkbox"] {
  accent-color: #58784f;
  width: 14px;
  height: 14px;
}
.status {
  position: absolute;
  bottom: 16px;
  left: 25px;
  right: 25px;
  display: flex;
  justify-content: space-between;
  font:
    10px ui-monospace,
    monospace;
  color: #84917d;
  pointer-events: none;
}
.status .snapping {
  color: #3c7043;
  font-weight: 700;
}
#toast {
  position: absolute;
  bottom: 80px;
  left: 50%;
  transform: translateX(-50%);
  background: #3e5543;
  color: white;
  padding: 10px 15px;
  border-radius: 7px;
  font-size: 11px;
  opacity: 0;
  pointer-events: none;
  max-width: 90%;
}
#toast.show {
  opacity: 1;
}
#material-menu {
  position: fixed;
  z-index: 20;
  width: min(330px, calc(100vw - 20px));
  max-height: calc(100dvh - 20px);
  overflow: auto;
  background: #fffefa;
  border: 1px solid #c9d2c1;
  border-radius: 12px;
  box-shadow: 0 15px 45px #34473125;
  padding: 15px;
}
.menu-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.menu-header strong {
  font-size: 13px;
}
.menu-header button {
  border: 0;
  background: transparent;
  font-size: 23px;
  padding: 0 3px;
}
#menu-note {
  font-size: 10px;
  line-height: 1.6;
  color: #8b9785;
  margin: 5px 0 10px;
}
#constants label {
  display: block;
  font-size: 11px;
  margin-top: 13px;
}
#constants label > span {
  float: right;
  color: #8a9684;
  font-size: 10px;
}
#constants input {
  display: block;
  width: 100%;
  border: 1px solid #d7ddcf;
  background: #f8f9f2;
  border-radius: 5px;
  padding: 8px;
  margin-top: 6px;
}
#constants small {
  display: block;
  margin-top: 5px;
  color: #919c8c;
  font-size: 9px;
  line-height: 1.5;
}
[hidden] {
  display: none !important;
}
@media (max-width: 720px) {
  header {
    padding: 0 12px;
    gap: 8px;
  }
  .subtitle {
    display: none;
  }
  .brand {
    font-size: 13px;
  }
  .status {
    left: 14px;
    right: 14px;
    font-size: 9px;
  }
}

#dimensions {
  font:
    10px ui-monospace,
    monospace;
  color: #62725c;
}
#belt-speed {
  width: 65px;
  padding: 3px;
  border: 1px solid var(--line);
  border-radius: 4px;
}
#keys-panel {
  position: fixed;
  z-index: 15;
  right: 20px;
  top: calc(var(--header-h) + 10px);
  width: min(440px, calc(100vw - 40px));
  max-height: calc(100dvh - 100px);
  overflow: auto;
  padding: 18px;
  background: #fffefa;
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: 0 10px 40px #34473125;
}
#keys-panel dl {
  display: grid;
  grid-template-columns: 115px 1fr;
  gap: 10px;
  font-size: 12px;
}
#keys-panel dt {
  font-weight: 600;
}
#keys-panel dd {
  margin: 0;
}
#keys-panel p {
  font-size: 11px;
  line-height: 1.6;
  color: #68785f;
}
.tools {
  max-width: calc(100% - 24px);
}

#settings-panel {
  position: fixed;
  z-index: 14;
  right: 16px;
  top: calc(var(--header-h) + 10px);
  width: min(380px, calc(100vw - 32px));
  max-height: calc(100dvh - 92px);
  overflow: auto;
  padding: 18px;
  background: #fffefa;
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: 0 10px 40px #34473125;
}
#settings-panel p,
#settings-panel small {
  font-size: 11px;
  line-height: 1.6;
  color: #73826a;
}
#settings-panel small {
  display: block;
  margin-bottom: 20px;
}
#settings-panel label {
  display: block;
  font-size: 12px;
  margin-top: 16px;
}
#settings-panel label span {
  float: right;
  color: #829078;
}
#settings-panel input {
  display: block;
  width: 100%;
  margin-top: 8px;
}
#settings-panel input[type="number"] {
  padding: 8px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: #f8f9f2;
}
#constants input[type="range"],
#settings-panel input[type="range"] {
  padding: 0;
  accent-color: #58784f;
  cursor: ew-resize;
  height: 20px;
  background: transparent;
  border: 0;
}

#settings-panel .setting-toggle {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 12px;
}
#settings-panel .setting-toggle input {
  width: 14px;
  margin: 0;
}

/* Always-visible centre marker, independent of browser datalist rendering. */
#constants select {
  display: block;
  width: 100%;
  padding: 8px;
  margin-top: 6px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: #f8f9f2;
}

:root {
  --ui-scale: 1;
  /* Compact top bar; floating panels open just below it. */
  --header-h: 46px;
  --panel: #fffefa;
  --canvas-bg: #f2f0e9;
}
:root[data-theme="dark"] {
  /* Darkened parchment neutrals (the light theme's paper, in shadow), with
     green kept for accents: active tools, toggles, Run, ground and walls. */
  color-scheme: dark;
  --ink: #ebe5d6;
  --line: #4a453b;
  --panel: #2a2722;
  --canvas-bg: #1c1a16;
  color: var(--ink);
  background: var(--canvas-bg);
}
header {
  height: calc(var(--header-h) * var(--ui-scale));
  background: var(--panel);
}
main {
  height: calc(100dvh - var(--header-h) * var(--ui-scale));
  background: var(--canvas-bg);
}
button,
select {
  background: var(--panel);
  color: var(--ink);
}
button:hover {
  background: color-mix(in srgb, var(--panel), #8aa17c 18%);
}
select {
  font: inherit;
  padding: 6px;
  border: 1px solid var(--line);
  border-radius: 5px;
  max-width: 100%;
}
.tools {
  top: 12px;
  gap: 4px;
  padding: 5px;
  width: max-content;
  max-width: calc(100% - 24px);
  flex-wrap: wrap;
  justify-content: center;
  background: var(--panel);
  zoom: var(--ui-scale);
}
.tools button {
  padding: 5px 7px;
}
.tool-settings {
  position: absolute;
  top: 96px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  background: var(--panel);
  border: 1px solid var(--line);
  padding: 9px 12px;
  border-radius: 9px;
  width: max-content;
  max-width: calc(100% - 24px);
  font-size: 11px;
  zoom: var(--ui-scale);
}
.tool-settings label {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  margin-right: 10px;
}
.tool-settings input[type="number"] {
  width: 60px;
}
#tool-help,
#impulse-options > span {
  opacity: 0.7;
}
.camera-controls {
  position: absolute;
  bottom: 54px;
  left: 16px;
  display: flex;
  align-items: center;
  gap: 2px;
  padding: 3px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 9px;
  zoom: var(--ui-scale);
}
.camera-controls button {
  min-width: 30px;
  height: 30px;
  padding: 0 6px;
  border-color: transparent;
  background: transparent;
}
.camera-controls .ui-icon {
  width: 18px;
  height: 18px;
  flex-basis: 18px;
}
.cluster-divider {
  align-self: stretch;
  margin: 3px 4px;
  border-left: 1px solid var(--line);
}
/* Checkbox kept focusable for keyboard and tests; the label is the toggle. */
.icon-toggle {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border: 1px solid transparent;
  border-radius: 7px;
  cursor: pointer;
  opacity: 0.6;
}
.icon-toggle input {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  margin: 0;
  opacity: 0;
  cursor: pointer;
}
.icon-toggle:hover {
  background: color-mix(in srgb, var(--panel), #8aa17c 18%);
}
.icon-toggle:has(input:checked) {
  opacity: 1;
  background: #e5eedf;
  border-color: #b6c9ad;
  color: #3e6237;
}
:root[data-theme="dark"] .icon-toggle:has(input:checked) {
  background: #3b4c3f;
  color: #ecf5e8;
  border-color: #768d70;
}
.icon-toggle:has(input:focus-visible) {
  outline: 2px solid #63876a;
  outline-offset: 1px;
}
.icon-toggle .ui-icon {
  width: 18px;
  height: 18px;
  flex-basis: 18px;
}
#zoom-level {
  min-width: 42px;
  text-align: center;
  font-size: 11px;
}
#settings-panel,
#keys-panel,
#presets-panel,
#clear-confirm,
#material-menu {
  background: var(--panel);
  color: var(--ink);
  zoom: var(--ui-scale);
}
:root[data-theme="dark"] #constants input,
:root[data-theme="dark"] #constants select,
:root[data-theme="dark"] #settings-panel input[type="number"] {
  background: #1c1a16;
  color: var(--ink);
}
:root[data-theme="dark"] .tools .active,
:root[data-theme="dark"] .edit-tools .active {
  background: #3b4c3f;
  color: #ecf5e8;
  border-color: #768d70;
}
:root[data-theme="dark"] .status {
  color: #bdb4a2;
}
#ui-size-value {
  float: right;
}
[hidden] {
  display: none !important;
}
@media (max-width: 700px) {
  .subtitle {
    display: none;
  }
  header {
    padding: 0 8px;
    gap: 6px;
  }
  .brand {
    font-size: 12px;
  }
  .playback {
    gap: 3px;
  }
  .playback button {
    padding: 6px;
  }
}
.brand,
.playback {
  zoom: var(--ui-scale);
}
#settings-panel,
#keys-panel,
#presets-panel {
  max-height: calc(
    (100dvh - (var(--header-h) + 26px) * var(--ui-scale)) / var(--ui-scale)
  );
}
#material-menu {
  max-height: calc((100dvh - 20px) / var(--ui-scale));
}
:root[data-theme="dark"] #settings-panel p,
:root[data-theme="dark"] #settings-panel small,
:root[data-theme="dark"] #constants small,
:root[data-theme="dark"] #menu-note,
:root[data-theme="dark"] #keys-panel p {
  color: #bdb4a2;
}
.ui-icon {
  width: 20px;
  height: 20px;
  flex: 0 0 20px;
  display: block;
  color: currentColor;
}
button[data-icon] {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 7px;
}
.tools button .ui-icon,
.edit-tools button .ui-icon {
  width: 22px;
  height: 22px;
  flex-basis: 22px;
}
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}
.debug-settings {
  margin: 24px 0 18px;
  padding: 12px;
  border: 1px dashed var(--line);
  border-radius: 8px;
}
.debug-settings summary {
  cursor: pointer;
  font-size: 12px;
}
#ui-icons {
  width: 100%;
  margin-top: 8px;
}
.edit-tools {
  position: absolute;
  top: 12px;
  left: 12px;
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding: 5px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 11px;
  box-shadow: 0 8px 30px #3b4b3610;
  zoom: var(--ui-scale);
}
.edit-tools button {
  padding: 7px;
  border-color: transparent;
  background: transparent;
}
.edit-tools button:hover {
  background: color-mix(in srgb, var(--panel), #8aa17c 18%);
}
.edit-tools .active {
  background: #e5eedf;
  border-color: #b6c9ad;
}
/* Drop-downs open over the tool-options strip below the toolbar. */
.tools {
  z-index: 3;
}
.tool-category {
  position: relative;
}
.category-toggle::after {
  content: "";
  border: 4px solid transparent;
  border-top-color: currentColor;
  margin: 4px 0 0 -2px;
  opacity: 0.6;
}
.category-menu {
  position: absolute;
  z-index: 5;
  top: calc(100% + 9px);
  left: -5px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: calc(100% + 10px);
  padding: 5px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 11px;
  box-shadow: 0 10px 30px #34473125;
}
.tools .category-menu button {
  justify-content: flex-start;
  padding-right: 14px;
}
/* Compact property row shared by the constants menu and settings panel. */
.prop-row {
  display: grid;
  grid-template-columns: 9.4em minmax(40px, 1fr) auto;
  align-items: center;
  gap: 8px;
  margin-top: 6px;
  font-size: 11px;
}
.prop-row > label {
  line-height: 1.25;
  cursor: help;
}
.prop-row .prop-value {
  display: inline-flex;
  align-items: center;
  gap: 4px;
}
.prop-row .unit {
  min-width: 2.6em;
  color: #8a9684;
  font-size: 10px;
}
:root[data-theme="dark"] .prop-row .unit {
  color: #bdb4a2;
}
#constants .prop-row input {
  display: block;
  margin: 0;
}
#constants .prop-row input[type="number"] {
  width: 58px;
  padding: 4px 5px;
}
#constants label.select-row {
  display: grid;
  grid-template-columns: 9.4em 1fr;
  align-items: center;
  gap: 8px;
  margin-top: 6px;
}
#constants label.select-row select {
  margin: 0;
  padding: 4px;
}
#constants .prop-row > label {
  margin: 0;
}
/* Settings panel: collapsible sections of compact rows. */
.settings-section {
  border-top: 1px solid var(--line);
  padding: 4px 0 8px;
}
.settings-section > summary {
  cursor: pointer;
  padding: 8px 0 4px;
  font-size: 12px;
  font-weight: 600;
}
#settings-panel .prop-row > label {
  margin: 0;
  font-size: 11px;
}
#settings-panel .prop-row input {
  margin: 0;
}
#settings-panel .prop-row input[type="number"] {
  width: 64px;
  padding: 4px 5px;
}
#settings-panel .prop-row .unit {
  float: none;
}
#settings-panel .setting-toggle {
  margin: 6px 0;
  font-size: 11px;
}
#settings-panel label.select-row {
  display: grid;
  grid-template-columns: 9.4em 1fr;
  align-items: center;
  gap: 8px;
  margin-top: 6px;
  font-size: 11px;
}
#settings-panel label.select-row select {
  width: 100%;
  margin: 0;
  padding: 4px;
}
#settings-panel #ui-size-value {
  float: none;
  min-width: 64px;
}
#settings-panel .button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 8px;
}
#settings-panel .button-row button {
  padding: 5px 9px;
  font-size: 11px;
}
#settings-panel .settings-section small {
  margin: 6px 0 0;
  font-size: 10px;
  line-height: 1.5;
}
#settings-panel > p {
  margin: 6px 0 8px;
}
#settings-panel .debug-settings {
  margin: 10px 0 4px;
  padding: 6px 10px;
}
#reset-settings {
  margin-top: 10px;
}
/* Centre detent for sliders centred on zero: short stubs above and below the
   track, hidden by the thumb when it sits on zero. */
.zero-slider {
  position: relative;
}
.zero-slider input[type="range"] {
  position: relative;
  z-index: 1;
  width: 100%;
  margin: 0;
}
.zero-tick {
  position: absolute;
  left: calc(50% - 0.5px);
  top: 0;
  bottom: 0;
  width: 1px;
  background: currentColor;
  opacity: 0.35;
  pointer-events: none;
}
#settings-panel .prop-row {
  grid-template-columns: 8.4em minmax(60px, 1fr) auto;
}
#settings-panel .prop-row input[type="number"] {
  width: 58px;
}
/* Selected-item panel: header row, then one row of toggles. */
#selection {
  position: absolute;
  right: 16px;
  bottom: 64px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  min-width: 190px;
  max-width: min(330px, calc(100% - 32px));
  padding: 6px 8px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 9px;
  font-size: 11px;
  zoom: var(--ui-scale);
}
.selection-header {
  display: flex;
  align-items: center;
  gap: 8px;
}
.selection-header strong {
  font-weight: 600;
  white-space: nowrap;
}
.header-actions {
  display: flex;
  margin-left: auto;
}
.row-caption {
  opacity: 0.7;
  margin-right: -4px;
}
.selection-header button {
  width: 28px;
  height: 28px;
  padding: 0;
  border-color: transparent;
  background: transparent;
}
.selection-header button .ui-icon {
  width: 18px;
  height: 18px;
  flex-basis: 18px;
}
.selection-header #delete {
  color: #a56c62;
}
.selection-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 4px 10px;
  padding-top: 6px;
  border-top: 1px solid var(--line);
}
.selection-row .switch {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  white-space: nowrap;
}
.selection-header button:hover {
  background: color-mix(in srgb, var(--panel), #8aa17c 18%);
}
:root[data-theme="dark"] #dimensions {
  color: #bdb4a2;
}
.header-divider {
  align-self: stretch;
  margin: 6px 2px;
  border-left: 1px solid var(--line);
}
button:disabled {
  opacity: 0.45;
  cursor: default;
}
/* Presets panel: grouped cards, each one loads its experiment. */
#presets-panel {
  position: fixed;
  z-index: 15;
  right: 16px;
  top: calc(var(--header-h) + 10px);
  width: min(420px, calc(100vw - 32px));
  overflow: auto;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: 0 10px 40px #34473125;
}
#presets-panel > p {
  margin: 6px 0 4px;
  font-size: 11px;
  line-height: 1.5;
  opacity: 0.8;
}
#preset-list h3 {
  margin: 14px 0 6px;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  opacity: 0.7;
}
#preset-list .preset {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  width: 100%;
  margin-top: 6px;
  padding: 8px 10px;
  text-align: left;
  font-size: 11px;
  line-height: 1.45;
}
#preset-list .preset strong {
  font-size: 12px;
}
#preset-list .preset-expect {
  color: #4f7547;
}
:root[data-theme="dark"] #preset-list .preset-expect {
  color: #a9c49d;
}
@media (max-width: 1150px) {
  .subtitle {
    display: none;
  }
}
/* When the header does not fit (narrow window or large GUI size; set by
   fitHeader() in app.js), header buttons keep their icon, tooltip and
   accessible name; only Run/Pause keeps its visible label. */
.compact-header .playback button > span {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
}
.compact-header .playback {
  gap: 4px;
}
.compact-header .subtitle {
  display: none;
}
#clear-confirm {
  position: fixed;
  z-index: 16;
  right: 16px;
  top: calc(var(--header-h) + 10px);
  width: min(300px, calc(100vw - 32px));
  padding: 14px 16px;
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: 0 10px 40px #34473125;
  font-size: 12px;
}
#clear-confirm p {
  margin: 6px 0 12px;
  font-size: 11px;
  line-height: 1.5;
  opacity: 0.85;
}
#clear-confirm .button-row {
  display: flex;
  justify-content: flex-end;
  gap: 8px;
}
#clear-confirm button {
  padding: 6px 12px;
  font-size: 11px;
}
#clear-confirm .danger {
  background: #a5544a;
  border-color: #a5544a;
  color: white;
}
#clear-confirm .danger:hover {
  background: #8e463d;
}
.cluster-scale {
  display: inline-flex;
  align-items: center;
  gap: 3px;
  margin-left: 2px;
  font-size: 10px;
  opacity: 0.85;
}
.cluster-scale input {
  width: 46px;
  padding: 3px 4px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: transparent;
  font-size: 11px;
}
/* Legend for velocity / net force arrows, above the view cluster. */
.vector-legend {
  position: absolute;
  left: 16px;
  bottom: 100px;
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding: 6px 9px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  font-size: 10px;
  pointer-events: none;
  zoom: var(--ui-scale);
}
.vector-legend > div {
  display: flex;
  align-items: center;
  gap: 6px;
}
.vector-legend small {
  opacity: 0.65;
  font-family: ui-monospace, monospace;
}
.swatch {
  position: relative;
  width: 22px;
  height: 2px;
  background: currentColor;
}
.swatch::after {
  content: "";
  position: absolute;
  right: -1px;
  top: -4px;
  border: 5px solid transparent;
  border-left: 7px solid currentColor;
  border-right: 0;
}
.swatch.velocity {
  color: #497caa;
}
.swatch.force {
  color: #c2410c;
}
:root[data-theme="dark"] .swatch.force {
  color: #ef8a6f;
}
/* Numeric readouts: tabular digits, right-aligned, so values do not jitter. */
.readout {
  border-top: 1px solid var(--line);
  padding-top: 4px;
}
.readout > summary,
.energy-panel > summary {
  cursor: pointer;
  font-weight: 600;
  font-size: 11px;
  padding: 2px 0;
}
.readout-grid {
  display: grid;
  grid-template-columns: auto 4.6em 4.6em auto;
  gap: 2px 6px;
  margin-top: 4px;
  font-size: 10.5px;
  align-items: baseline;
}
.num {
  text-align: right;
  font-family: ui-monospace, monospace;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}
.readout-grid .unit,
.energy-rows .unit {
  opacity: 0.65;
  font-size: 10px;
}
.energy-panel {
  position: absolute;
  top: 12px;
  right: 16px;
  width: 240px;
  padding: 6px 10px 8px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 9px;
  font-size: 10.5px;
  zoom: var(--ui-scale);
}
.energy-panel > summary .energy-total {
  float: right;
  font-family: ui-monospace, monospace;
  font-variant-numeric: tabular-nums;
}
.energy-bar {
  display: flex;
  height: 8px;
  margin: 6px 0;
  overflow: hidden;
  border-radius: 4px;
  background: color-mix(in srgb, var(--line), transparent 50%);
}
.energy-bar span {
  height: 100%;
}
.energy-rows {
  display: grid;
  grid-template-columns: 10px 1fr 4.6em auto;
  gap: 2px 6px;
  align-items: center;
}
.key {
  width: 10px;
  height: 10px;
  border-radius: 2px;
}
.kinetic {
  background: #497caa;
}
.gravitational {
  background: #6d8f5f;
}
.elastic {
  background: #c99a3e;
}
.electric {
  background: #b0577f;
}
.energy-bar .negative {
  background-image: repeating-linear-gradient(
    135deg,
    transparent 0 3px,
    #ffffff80 3px 5px
  );
}
.graph-panel {
  border-top: 1px solid var(--line);
  padding-top: 4px;
}
.graph-panel > summary {
  cursor: pointer;
  font-weight: 600;
  font-size: 11px;
  padding: 2px 0;
}
#selection label.select-row {
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 8px;
  margin: 4px 0;
}
#graph-canvas {
  display: block;
  width: 100%;
  height: 130px;
}
.field-work {
  display: grid;
  grid-template-columns: 1fr 4.6em auto;
  gap: 1px 6px;
  margin: 2px 0 6px;
  padding: 4px 0;
  border-bottom: 1px dashed var(--line);
  align-items: baseline;
}
.field-work .unit {
  opacity: 0.65;
  font-size: 10px;
}
.field-work > span:nth-child(4),
.field-work > span:nth-child(5) {
  font-weight: 600;
}
.playback button {
  white-space: nowrap;
}
#speed {
  font-size: 11px;
  padding: 0 4px;
  border-radius: 7px;
}
:root[data-theme="dark"] .tools {
  border-color: var(--line);
}
/* Data colours re-stepped for the dark surface (validated as a stacked bar:
   lightness, chroma, adjacent colour-blind separation, 3:1 contrast). */
:root[data-theme="dark"] .kinetic {
  background: #3987e5;
}
:root[data-theme="dark"] .gravitational {
  background: #199e70;
}
:root[data-theme="dark"] .elastic {
  background: #c98500;
}
:root[data-theme="dark"] .electric {
  background: #d55181;
}
:root[data-theme="dark"] .swatch.velocity {
  color: #6fa8ec;
}
/* Compact top bar: smaller buttons, icons and brand. */
header {
  padding: 0 14px;
  gap: 14px;
}
.brand {
  gap: 8px;
  font-size: 14px;
}
.brand > span {
  font-size: 24px;
}
.playback {
  gap: 5px;
}
.playback button {
  padding: 4px 9px;
  min-height: 30px;
  border-radius: 6px;
}
.playback .ui-icon {
  width: 17px;
  height: 17px;
  flex-basis: 17px;
}
#pause {
  min-width: 40px;
}
#speed {
  height: 30px;
}
.header-divider {
  margin: 4px 1px;
}
.preset-preview {
  flex: 0 0 112px;
  width: 112px;
  height: 72px;
  border: 1px solid var(--line);
  border-radius: 6px;
}
.preset-text {
  display: flex;
  flex-direction: column;
  gap: 3px;
  min-width: 0;
}
/* Clear scene is destructive: red, like its confirmation button. */
#clear {
  background: #a5544a;
  border-color: #a5544a;
  color: white;
}
#clear:hover {
  background: #8e463d;
}
:root[data-theme="dark"] #clear {
  background: #b35d52;
  border-color: #b35d52;
}
:root[data-theme="dark"] #clear:hover {
  background: #c46b5f;
}
#speed {
  width: 62px;
}
/* Site navigation: the drop-down beside the brand that switches between the
   simulations. Its entries are ordinary links. */
.site-nav {
  position: relative;
  zoom: var(--ui-scale);
}
.nav-toggle {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 30px;
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 12px;
  white-space: nowrap;
}
.nav-toggle::after {
  content: "";
  border: 4px solid transparent;
  border-top-color: currentColor;
  margin-top: 4px;
  opacity: 0.6;
}
.nav-menu {
  position: absolute;
  z-index: 30;
  top: calc(100% + 8px);
  left: 0;
  display: flex;
  flex-direction: column;
  gap: 2px;
  width: max-content;
  max-width: min(300px, calc(100vw - 24px));
  padding: 5px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 11px;
  box-shadow: 0 10px 30px #34473125;
}
.nav-menu a {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 7px 10px;
  border: 1px solid transparent;
  border-radius: 7px;
  color: var(--ink);
  text-decoration: none;
  font-size: 12px;
}
.nav-menu a:hover {
  background: color-mix(in srgb, var(--panel), #8aa17c 18%);
}
.nav-menu a:focus-visible {
  outline: 2px solid #63876a;
  outline-offset: 1px;
}
.nav-menu a[aria-current="page"] {
  background: #e5eedf;
  border-color: #b6c9ad;
}
:root[data-theme="dark"] .nav-menu a[aria-current="page"] {
  background: #3b4c3f;
  border-color: #768d70;
}
.nav-menu small {
  font-size: 10.5px;
  opacity: 0.7;
}
@media (max-width: 700px) {
  .nav-toggle {
    padding: 4px 7px;
    font-size: 11px;
  }
}