/* FIELDLAB visual system */
:root {
  color-scheme: light;
  --ink: #17201f;
  --ink-soft: #34413f;
  --muted: #687370;
  --line: #d9dfdc;
  --line-strong: #b7c0bc;
  --paper: #ffffff;
  --page: #f2f4f2;
  --wash: #e9eeeb;
  --canvas: #101817;
  --canvas-raised: #182422;
  --canvas-line: #2b3835;
  --coral: #e65d45;
  --coral-dark: #ae3e2d;
  --coral-soft: #fdeae6;
  --teal: #138f7a;
  --teal-dark: #086554;
  --teal-soft: #def3ed;
  --yellow: #d6a824;
  --yellow-dark: #7f6208;
  --yellow-soft: #fff5cc;
  --focus: #086b5d;
  --shadow-tool: 0 14px 36px rgb(23 32 31 / 10%);
  --radius-xs: 3px;
  --radius-sm: 5px;
  --radius: 8px;
  --content: 1440px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 92px;
}

body {
  min-width: 320px;
  margin: 0;
  background: var(--page);
  color: var(--ink);
  font-family: "Segoe UI", "Microsoft YaHei UI", "Microsoft YaHei", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.6;
  letter-spacing: 0;
  text-rendering: optimizeLegibility;
}

button,
input,
select,
textarea {
  font: inherit;
  letter-spacing: 0;
}

button,
a,
input,
summary {
  -webkit-tap-highlight-color: transparent;
}

button {
  color: inherit;
}

button:not(:disabled),
summary,
input[type="range"],
input[type="checkbox"],
input[type="radio"] {
  cursor: pointer;
}

img,
canvas {
  display: block;
  max-width: 100%;
}

[hidden] {
  display: none !important;
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
}

h1,
h2,
h3,
h4 {
  line-height: 1.18;
  letter-spacing: 0;
}

h1 {
  margin-bottom: 12px;
  font-size: 44px;
  font-weight: 760;
}

h2 {
  margin-bottom: 0;
  font-size: 30px;
  font-weight: 760;
}

h3 {
  margin-bottom: 9px;
  font-size: 20px;
  font-weight: 720;
}

h4 {
  margin-bottom: 0;
  font-size: 16px;
  font-weight: 720;
}

a {
  color: inherit;
}

code {
  padding: 1px 4px;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  background: var(--page);
  color: var(--ink);
  font-family: Consolas, "Courier New", monospace;
  font-size: 0.92em;
}

sup,
sub {
  line-height: 0;
}

::selection {
  background: var(--yellow-soft);
  color: var(--ink);
}

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  z-index: 1000;
  top: 10px;
  left: 10px;
  transform: translateY(-150%);
  padding: 9px 14px;
  border-radius: var(--radius-sm);
  background: var(--paper);
  color: var(--ink);
  font-weight: 700;
  box-shadow: var(--shadow-tool);
}

.skip-link:focus {
  transform: translateY(0);
}

.sr-only {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}

.site-shell {
  width: 100%;
  overflow: clip;
}

.topbar {
  position: sticky;
  z-index: 100;
  top: 0;
  display: flex;
  min-height: 72px;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
  padding: 10px max(24px, calc((100% - var(--content)) / 2));
  border-bottom: 1px solid #26322f;
  background: rgb(23 32 31 / 97%);
  color: var(--paper);
  backdrop-filter: blur(12px);
}

.brand-lockup,
.brand,
.chapter-meta,
.progress-copy,
.toolbar-group,
.toolbar-actions,
.visual-header,
.visual-footer,
.simulation-status,
.range-heading,
.panel-section-heading,
.live-badge,
.quiz-actions,
.site-footer {
  display: flex;
  align-items: center;
}

.brand-lockup {
  min-width: 0;
  gap: 17px;
}

.brand {
  flex: 0 0 auto;
  gap: 8px;
  color: var(--paper);
  text-decoration: none;
}

.brand-mark {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border: 1px solid var(--teal);
  border-radius: var(--radius-sm);
  color: #6fe0c5;
  font-family: Georgia, serif;
  font-size: 26px;
  line-height: 1;
}

.brand-name {
  font-size: 21px;
  font-weight: 800;
}

.brand-code {
  color: #b8c4c1;
  font-family: Consolas, "Courier New", monospace;
  font-size: 12px;
  font-weight: 700;
}

.brand-rule {
  width: 1px;
  height: 33px;
  background: #46534f;
}

.chapter-meta {
  min-width: 0;
  align-items: flex-start;
  flex-direction: column;
  gap: 0;
}

.chapter-meta .eyebrow {
  color: #9ca9a5;
  font-size: 10px;
  font-weight: 700;
}

.chapter-meta strong {
  overflow: hidden;
  max-width: 260px;
  font-size: 13px;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chapter-progress-wrap {
  width: min(260px, 26vw);
  flex: 0 0 auto;
}

.progress-copy {
  justify-content: space-between;
  margin-bottom: 5px;
  color: #b8c4c1;
  font-size: 11px;
}

.progress-copy strong {
  color: var(--paper);
  font-family: Consolas, "Courier New", monospace;
  font-size: 12px;
}

.progress-meter {
  display: block;
  width: 100%;
  height: 3px;
  overflow: hidden;
  border: 0;
  background: #3f4c48;
  color: var(--coral);
  appearance: none;
}

.progress-meter::-webkit-progress-bar {
  background: #3f4c48;
}

.progress-meter::-webkit-progress-value,
.progress-meter::-moz-progress-bar {
  background: var(--coral);
  transition: width 250ms ease;
}

.intro-strip,
.lab-section,
.content-section,
.rigor-note,
.site-footer {
  width: min(calc(100% - 48px), var(--content));
  margin-inline: auto;
}

.intro-strip {
  display: grid;
  grid-template-columns: minmax(0, 1.7fr) minmax(300px, 0.7fr);
  gap: 64px;
  align-items: end;
  padding-block: 48px 40px;
}

.section-kicker,
.panel-kicker,
.item-label {
  text-transform: uppercase;
}

.section-kicker {
  margin-bottom: 10px;
  color: var(--muted);
  font-family: Consolas, "Courier New", monospace;
  font-size: 11px;
  font-weight: 700;
}

.kicker-index {
  display: inline-grid;
  min-width: 34px;
  height: 21px;
  margin-right: 8px;
  place-items: center;
  border-radius: var(--radius-xs);
  background: var(--ink);
  color: var(--paper);
}

.intro-lede {
  max-width: 690px;
  margin-bottom: 0;
  color: var(--ink-soft);
  font-size: 18px;
}

.intro-note {
  display: grid;
  grid-template-columns: 42px 1fr;
  gap: 14px;
  align-items: start;
  padding: 18px 0 3px 20px;
  border-left: 3px solid var(--yellow);
}

.intro-note p {
  margin-bottom: 0;
  color: var(--muted);
  font-size: 13px;
}

.intro-note strong {
  color: var(--ink);
  font-size: 14px;
}

.note-symbol {
  display: grid;
  width: 40px;
  height: 40px;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  color: var(--yellow-dark);
  font-family: Georgia, serif;
  font-size: 22px;
}

.lab-section {
  padding-bottom: 72px;
}

.section-heading {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 40px;
  padding: 24px 0 20px;
  border-top: 1px solid var(--line-strong);
}

.section-heading .section-kicker {
  margin-bottom: 6px;
}

.section-description {
  max-width: 520px;
  margin-bottom: 3px;
  color: var(--muted);
  font-size: 14px;
  text-align: right;
}

.experiment-toolbar {
  display: grid;
  grid-template-columns: minmax(460px, 1fr) auto auto;
  gap: 22px;
  align-items: end;
  padding: 16px 18px;
  border: 1px solid #2d3936;
  border-bottom: 0;
  border-radius: var(--radius) var(--radius) 0 0;
  background: var(--ink);
  color: var(--paper);
}

.toolbar-group {
  min-width: 0;
  align-items: stretch;
  flex-wrap: wrap;
  gap: 7px;
}

.toolbar-label {
  flex-basis: 100%;
  margin-bottom: 1px;
  color: #9ba8a4;
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
}

.preset-button,
.segment-button,
.icon-button,
.outline-button,
.primary-button,
.text-button,
.link-button {
  border: 0;
  border-radius: var(--radius-sm);
  background: transparent;
  font-weight: 700;
}

.preset-button {
  display: inline-flex;
  min-height: 38px;
  align-items: center;
  gap: 5px;
  padding: 7px 10px;
  border: 1px solid #43504c;
  color: #dce3e0;
  font-size: 12px;
}

.preset-button:hover,
.preset-button.is-active,
.preset-button[aria-pressed="true"] {
  border-color: #78847f;
  background: #2b3734;
  color: var(--paper);
}

.preset-button.is-active,
.preset-button[aria-pressed="true"] {
  box-shadow: inset 0 -2px var(--yellow);
}

.charge-glyph {
  display: inline-grid;
  width: 18px;
  height: 18px;
  flex: 0 0 auto;
  place-items: center;
  border: 1px solid currentColor;
  border-radius: 50%;
  font-size: 13px;
  line-height: 1;
}

.charge-glyph + .charge-glyph {
  margin-left: -9px;
}

.charge-glyph-positive,
.charge-indicator-positive {
  color: #ff8d78;
}

.charge-glyph-negative,
.charge-indicator-negative {
  color: #5bd9bd;
}

.charge-glyph-neutral {
  color: #e6c863;
}

.segmented-control {
  display: grid;
  grid-template-columns: 1fr 1fr;
  overflow: hidden;
  border: 1px solid #43504c;
  border-radius: var(--radius-sm);
}

.segment-button {
  min-height: 38px;
  padding: 7px 12px;
  border-radius: 0;
  color: #abb7b3;
  font-size: 12px;
  white-space: nowrap;
}

.segment-button + .segment-button {
  border-left: 1px solid #43504c;
}

.segment-button:hover,
.segment-button.is-active,
.segment-button[aria-pressed="true"] {
  background: var(--paper);
  color: var(--ink);
}

.toolbar-actions {
  gap: 6px;
}

.icon-button {
  display: inline-grid;
  min-width: 50px;
  min-height: 48px;
  place-items: center;
  padding: 4px 7px;
  border: 1px solid #43504c;
  color: #bac5c2;
  font-size: 10px;
}

.icon-button > span:first-child {
  color: var(--paper);
  font-family: Consolas, "Courier New", monospace;
  font-size: 18px;
  line-height: 1;
}

.icon-button:hover {
  border-color: #74817c;
  background: #2b3734;
  color: var(--paper);
}

.icon-button-accent {
  border-color: #b79728;
  background: var(--yellow);
  color: #312703;
}

.icon-button-accent > span:first-child {
  color: #312703;
}

.experiment-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(320px, 370px);
  align-items: stretch;
  border: 1px solid #2d3936;
  border-radius: 0 0 var(--radius) var(--radius);
  background: var(--paper);
  box-shadow: var(--shadow-tool);
}

.visual-panel {
  min-width: 0;
  padding: 20px;
  border-radius: 0 0 0 var(--radius);
  background: var(--canvas);
  color: var(--paper);
}

.visual-header {
  min-height: 54px;
  justify-content: space-between;
  gap: 20px;
  padding-bottom: 14px;
}

.panel-kicker {
  margin-bottom: 3px;
  color: #8f9d99;
  font-family: Consolas, "Courier New", monospace;
  font-size: 9px;
  font-weight: 700;
}

.visual-header h3 {
  margin-bottom: 0;
  font-size: 19px;
}

.simulation-status {
  flex: 0 0 auto;
  gap: 7px;
  padding: 5px 8px;
  border: 1px solid #35423e;
  border-radius: var(--radius-xs);
  color: #b8c5c1;
  font-size: 10px;
}

.status-dot {
  display: inline-block;
  width: 7px;
  height: 7px;
  flex: 0 0 auto;
  border: 1px solid #68d4ba;
  border-radius: 50%;
  background: var(--teal);
  box-shadow: 0 0 0 3px rgb(19 143 122 / 13%);
}

.canvas-stage {
  position: relative;
  isolation: isolate;
  width: 100%;
  overflow: hidden;
  border: 1px solid #3a4743;
  border-radius: var(--radius-sm);
  aspect-ratio: 15 / 9;
  background-color: #131d1b;
  background-image:
    linear-gradient(rgb(255 255 255 / 4%) 1px, transparent 1px),
    linear-gradient(90deg, rgb(255 255 255 / 4%) 1px, transparent 1px),
    linear-gradient(rgb(255 255 255 / 2%) 1px, transparent 1px),
    linear-gradient(90deg, rgb(255 255 255 / 2%) 1px, transparent 1px);
  background-position: center;
  background-size: 80px 80px, 80px 80px, 20px 20px, 20px 20px;
}

.canvas-stage::before,
.canvas-stage::after {
  position: absolute;
  z-index: 0;
  content: "";
  pointer-events: none;
}

.canvas-stage::before {
  top: 50%;
  right: 0;
  left: 0;
  border-top: 1px solid rgb(255 255 255 / 14%);
}

.canvas-stage::after {
  top: 0;
  bottom: 0;
  left: 50%;
  border-left: 1px solid rgb(255 255 255 / 14%);
}

.canvas-stage canvas {
  position: absolute;
  z-index: 1;
  inset: 0;
  width: 100%;
  height: 100%;
  touch-action: none;
}

.canvas-grid-label {
  position: absolute;
  z-index: 2;
  color: rgb(221 232 228 / 48%);
  font-family: Consolas, "Courier New", monospace;
  font-size: 9px;
  pointer-events: none;
}

.canvas-grid-label-x {
  right: 9px;
  bottom: 48%;
}

.canvas-grid-label-y {
  top: 8px;
  left: calc(50% + 8px);
}

.canvas-hint,
.canvas-badge {
  position: absolute;
  z-index: 3;
  display: flex;
  align-items: center;
  border: 1px solid #44514d;
  border-radius: var(--radius-xs);
  background: rgb(16 24 23 / 88%);
  color: #d7e1de;
  pointer-events: none;
  backdrop-filter: blur(5px);
}

.canvas-hint {
  bottom: 12px;
  left: 12px;
  gap: 7px;
  max-width: calc(100% - 250px);
  padding: 7px 10px;
  font-size: 10px;
}

.hint-symbol {
  color: var(--yellow);
  font-family: Consolas, "Courier New", monospace;
  font-size: 16px;
}

.canvas-badge {
  top: 12px;
  right: 12px;
  padding: 6px 9px;
  color: #a9b6b2;
  font-family: Consolas, "Courier New", monospace;
  font-size: 9px;
}

.canvas-badge strong {
  color: var(--paper);
  font-size: 10px;
}

.canvas-empty-state {
  position: absolute;
  z-index: 4;
  top: 50%;
  left: 50%;
  display: grid;
  width: min(280px, 80%);
  transform: translate(-50%, -50%);
  justify-items: center;
  padding: 20px;
  border: 1px solid #43504c;
  border-radius: var(--radius-sm);
  background: var(--canvas-raised);
  color: #95a29e;
  text-align: center;
  font-size: 11px;
}

.canvas-empty-state > span:first-child {
  color: var(--yellow);
  font-size: 25px;
}

.canvas-empty-state strong {
  color: var(--paper);
  font-size: 13px;
}

.visual-footer {
  min-height: 58px;
  justify-content: space-between;
  gap: 20px;
  padding-top: 13px;
}

.legend {
  display: flex;
  min-width: 0;
  align-items: center;
  flex-wrap: wrap;
  gap: 7px 15px;
}

.legend-label,
.readout-label {
  color: #8e9c98;
  font-family: Consolas, "Courier New", monospace;
  font-size: 9px;
  text-transform: uppercase;
}

.legend-item {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: #c2ceca;
  font-size: 10px;
  white-space: nowrap;
}

.legend-swatch {
  display: inline-block;
  width: 9px;
  height: 9px;
  border: 2px solid var(--canvas);
  border-radius: 50%;
  outline: 1px solid currentColor;
}

.swatch-positive {
  background: var(--coral);
  color: #ff806b;
}

.swatch-negative {
  background: var(--teal);
  color: #52d8ba;
}

.legend-line {
  display: inline-block;
  width: 19px;
  height: 5px;
  border-top: 2px solid;
}

.legend-line-field {
  border-color: #eef4f2;
}

.legend-line-equipotential {
  border-color: var(--yellow);
  border-top-style: dashed;
}

.canvas-readout {
  display: flex;
  flex: 0 0 auto;
  align-items: flex-end;
  flex-direction: column;
  line-height: 1.25;
}

.canvas-readout strong {
  min-width: 55px;
  color: #f1ca59;
  font-family: Consolas, "Courier New", monospace;
  font-size: 13px;
  text-align: right;
}

.visual-caption {
  margin: 0;
  padding-top: 10px;
  border-top: 1px solid #2a3532;
  color: #7f8d89;
  font-size: 10px;
}

.control-panel {
  min-width: 0;
  border-left: 1px solid var(--line);
  border-radius: 0 0 var(--radius) 0;
  background: var(--paper);
  color: var(--ink);
}

.panel-tabs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  height: 49px;
  border-bottom: 1px solid var(--line);
}

.panel-tab {
  position: relative;
  border: 0;
  border-right: 1px solid var(--line);
  background: #f8f9f8;
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
}

.panel-tab:last-child {
  border-right: 0;
}

.panel-tab:hover {
  color: var(--ink);
}

.panel-tab.is-active,
.panel-tab[aria-selected="true"] {
  background: var(--paper);
  color: var(--ink);
}

.panel-tab.is-active::after,
.panel-tab[aria-selected="true"]::after {
  position: absolute;
  right: 18px;
  bottom: -1px;
  left: 18px;
  height: 3px;
  background: var(--coral);
  content: "";
}

.tab-panels {
  min-height: 620px;
}

.tab-panel {
  padding: 0 18px;
}

.panel-section {
  padding: 18px 0;
  border-bottom: 1px solid var(--line);
}

.panel-section:last-child {
  border-bottom: 0;
}

.panel-section-heading {
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 14px;
}

.panel-section-heading .panel-kicker {
  color: #74807d;
}

.unit-note {
  color: var(--muted);
  font-size: 9px;
}

.range-control + .range-control {
  margin-top: 17px;
}

.range-heading {
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 6px;
}

.range-heading label {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  font-size: 12px;
  font-weight: 700;
}

.range-heading output {
  min-width: 72px;
  padding: 3px 6px;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  background: var(--page);
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
  font-weight: 700;
  text-align: right;
}

.charge-indicator,
.probe-indicator {
  display: inline-grid;
  width: 20px;
  height: 20px;
  place-items: center;
  border: 1px solid currentColor;
  border-radius: 50%;
  font-size: 13px;
  line-height: 1;
}

.charge-indicator-positive {
  background: var(--coral-soft);
  color: var(--coral-dark);
}

.charge-indicator-negative {
  background: var(--teal-soft);
  color: var(--teal-dark);
}

.probe-indicator {
  background: var(--yellow-soft);
  color: var(--yellow-dark);
  font-size: 20px;
}

input[type="range"] {
  width: 100%;
  height: 18px;
  margin: 0;
  appearance: none;
  background: transparent;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: 4px;
  border-radius: 2px;
  background: linear-gradient(90deg, var(--teal) 0 48%, #cfd5d2 48% 52%, var(--coral) 52% 100%);
}

input[type="range"]::-moz-range-track {
  height: 4px;
  border: 0;
  border-radius: 2px;
  background: linear-gradient(90deg, var(--teal) 0 48%, #cfd5d2 48% 52%, var(--coral) 52% 100%);
}

input[type="range"]::-webkit-slider-thumb {
  width: 17px;
  height: 17px;
  margin-top: -7px;
  appearance: none;
  border: 3px solid var(--paper);
  border-radius: 50%;
  background: var(--ink);
  box-shadow: 0 0 0 1px var(--ink);
}

input[type="range"]::-moz-range-thumb {
  width: 12px;
  height: 12px;
  border: 3px solid var(--paper);
  border-radius: 50%;
  background: var(--ink);
  box-shadow: 0 0 0 1px var(--ink);
}

input[type="range"]:focus-visible {
  outline: 0;
}

input[type="range"]:focus-visible::-webkit-slider-thumb {
  box-shadow: 0 0 0 1px var(--ink), 0 0 0 5px rgb(19 143 122 / 28%);
}

input[type="range"]:focus-visible::-moz-range-thumb {
  box-shadow: 0 0 0 1px var(--ink), 0 0 0 5px rgb(19 143 122 / 28%);
}

.range-scale {
  display: flex;
  justify-content: space-between;
  color: #89938f;
  font-family: Consolas, "Courier New", monospace;
  font-size: 8px;
}

.text-button {
  padding: 3px 0;
  color: var(--teal-dark);
  font-size: 10px;
  text-decoration: underline;
  text-decoration-color: rgb(8 101 84 / 35%);
  text-underline-offset: 3px;
}

.text-button:hover {
  color: var(--ink);
}

.check-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 7px;
}

.check-row,
.radio-row {
  position: relative;
  display: flex;
  min-width: 0;
  min-height: 34px;
  align-items: center;
  gap: 8px;
  padding: 6px 8px;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  color: var(--ink-soft);
  font-size: 11px;
  font-weight: 650;
}

.check-row:hover,
.radio-row:hover {
  border-color: var(--line-strong);
  background: var(--page);
}

.check-row input,
.radio-row input {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
}

.check-mark {
  position: relative;
  width: 15px;
  height: 15px;
  flex: 0 0 auto;
  border: 1px solid var(--line-strong);
  border-radius: 2px;
  background: var(--paper);
}

.check-row input:checked + .check-mark {
  border-color: var(--teal-dark);
  background: var(--teal);
}

.check-row input:checked + .check-mark::after {
  position: absolute;
  top: 1px;
  left: 4px;
  width: 4px;
  height: 8px;
  transform: rotate(45deg);
  border: solid var(--paper);
  border-width: 0 2px 2px 0;
  content: "";
}

.check-row:has(input:focus-visible),
.radio-row:has(input:focus-visible) {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

.path-controls {
  min-width: 0;
  margin: 0;
  border: 0;
}

.path-controls legend {
  width: 100%;
  padding: 0;
}

.path-controls legend > span {
  display: flex;
  align-items: flex-start;
  flex-direction: column;
}

.path-controls legend strong {
  font-size: 16px;
}

.radio-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 7px;
}

.radio-row {
  justify-content: center;
}

.radio-mark {
  position: relative;
  width: 14px;
  height: 14px;
  flex: 0 0 auto;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
}

.radio-row input:checked + .radio-mark {
  border-color: var(--coral);
}

.radio-row input:checked + .radio-mark::after {
  position: absolute;
  inset: 3px;
  border-radius: 50%;
  background: var(--coral);
  content: "";
}

.panel-footnote {
  margin: 0 18px;
  padding: 13px 0 15px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 9px;
}

.panel-footnote > span {
  display: inline-grid;
  width: 15px;
  height: 15px;
  margin-right: 5px;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  font-family: Georgia, serif;
  font-size: 10px;
}

.live-badge {
  gap: 6px;
  color: var(--teal-dark);
  font-size: 10px;
  font-weight: 700;
}

.reading-list {
  border-top: 2px solid var(--ink);
}

.reading-row {
  display: grid;
  grid-template-columns: 1fr minmax(110px, auto);
  gap: 12px;
  align-items: baseline;
  padding: 10px 0;
  border-bottom: 1px solid var(--line);
}

.reading-row > span {
  color: var(--muted);
  font-size: 11px;
}

.reading-row output {
  color: var(--ink);
  font-family: Consolas, "Courier New", monospace;
  font-size: 12px;
  font-weight: 700;
  text-align: right;
}

.reading-row:first-child output,
.reading-row:nth-child(2) output {
  color: var(--coral-dark);
}

.measurement-summary {
  margin: 12px 0 0;
  padding: 9px;
  border-left: 3px solid var(--yellow);
  background: var(--yellow-soft);
  color: #615219;
  font-size: 10px;
}

.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
}

.measurement-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 10px;
}

.measurement-table th,
.measurement-table td {
  padding: 7px 8px;
  border-bottom: 1px solid var(--line);
  text-align: right;
  white-space: nowrap;
}

.measurement-table th:first-child,
.measurement-table td:first-child {
  text-align: left;
}

.measurement-table th {
  background: var(--page);
  color: var(--muted);
  font-weight: 700;
}

.measurement-table tr:last-child td {
  border-bottom: 0;
}

.measurement-table .empty-row td {
  padding-block: 22px;
  color: var(--muted);
  text-align: center;
}

.outline-button,
.primary-button {
  min-height: 38px;
  padding: 8px 13px;
  border: 1px solid var(--ink);
  font-size: 11px;
}

.outline-button:hover {
  background: var(--ink);
  color: var(--paper);
}

.full-width {
  width: 100%;
  margin-top: 10px;
}

.principle-lead > p:not(.panel-kicker):not(.formula-note) {
  color: var(--ink-soft);
  font-size: 12px;
}

.formula-block {
  display: flex;
  min-height: 94px;
  align-items: center;
  justify-content: center;
  gap: 15px;
  margin: 14px 0 11px;
  border-block: 1px solid var(--line);
  background: var(--page);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 28px;
  font-style: italic;
}

.formula-fraction {
  display: inline-grid;
  min-width: 75px;
  text-align: center;
}

.formula-fraction i,
.formula-fraction em {
  padding: 1px 6px;
  font-weight: 400;
}

.formula-fraction i {
  border-bottom: 1px solid var(--ink);
}

.formula-note {
  margin-bottom: 0;
  color: var(--muted);
  font-size: 9px;
}

.principle-line {
  display: grid;
  grid-template-columns: 30px 1fr;
  gap: 10px;
  align-items: start;
  padding: 9px 0;
  border-bottom: 1px solid var(--line);
}

.principle-line:last-child {
  border-bottom: 0;
}

.principle-symbol {
  padding-top: 2px;
  color: var(--coral-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
  font-weight: 700;
}

.principle-line p {
  margin-bottom: 0;
  color: var(--muted);
  font-size: 11px;
}

.principle-line strong {
  color: var(--ink);
}

.content-section {
  padding-block: 64px;
}

.content-section + .content-section {
  border-top: 1px solid var(--line-strong);
}

.compact-heading {
  padding-top: 0;
  border-top: 0;
}

.guided-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  border-top: 2px solid var(--ink);
  border-left: 1px solid var(--line);
}

.guided-item {
  position: relative;
  display: grid;
  min-height: 238px;
  grid-template-columns: 43px minmax(0, 1fr) 72px;
  gap: 18px;
  padding: 24px;
  overflow: hidden;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}

.item-index,
.knowledge-number,
.question-number,
.summary-number {
  font-family: Consolas, "Courier New", monospace;
  font-weight: 700;
}

.item-index {
  color: var(--coral-dark);
  font-size: 12px;
}

.item-label {
  margin-bottom: 6px;
  color: var(--muted);
  font-family: Consolas, "Courier New", monospace;
  font-size: 9px;
  font-weight: 700;
}

.guided-content p:not(.item-label) {
  max-width: 480px;
  margin-bottom: 16px;
  color: var(--muted);
  font-size: 13px;
}

.link-button {
  padding: 0;
  color: var(--teal-dark);
  font-size: 11px;
}

.link-button:hover,
.knowledge-link:hover {
  color: var(--coral-dark);
}

.link-button span,
.knowledge-link span {
  display: inline-block;
  transition: transform 150ms ease;
}

.link-button:hover span,
.knowledge-link:hover span {
  transform: translateX(3px);
}

.item-symbol {
  display: grid;
  width: 64px;
  height: 64px;
  place-items: center;
  align-self: center;
  border: 1px solid currentColor;
  border-radius: 50%;
  font-family: Consolas, "Courier New", monospace;
  font-size: 23px;
  font-weight: 400;
}

.symbol-positive {
  background: var(--coral-soft);
  color: var(--coral-dark);
}

.symbol-dipole,
.symbol-equipotential {
  background: var(--teal-soft);
  color: var(--teal-dark);
}

.symbol-same {
  background: var(--yellow-soft);
  color: var(--yellow-dark);
}

.knowledge-section {
  width: 100%;
  max-width: none;
  padding-inline: max(24px, calc((100% - var(--content)) / 2));
  background: var(--ink);
  color: var(--paper);
}

.knowledge-section .section-heading {
  width: min(100%, var(--content));
  margin-inline: auto;
}

.knowledge-section .section-kicker,
.knowledge-section .section-description {
  color: #aab7b3;
}

.knowledge-section .kicker-index {
  background: var(--yellow);
  color: #312703;
}

.knowledge-grid {
  display: grid;
  width: min(100%, var(--content));
  margin-inline: auto;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  border-top: 1px solid #596560;
  border-left: 1px solid #3c4945;
}

.knowledge-item {
  min-height: 270px;
  padding: 22px;
  border-right: 1px solid #3c4945;
  border-bottom: 1px solid #3c4945;
}

.knowledge-number {
  display: block;
  margin-bottom: 36px;
  color: #83908c;
  font-size: 11px;
}

.knowledge-item .item-label {
  color: #96a39f;
}

.knowledge-item h3 {
  color: var(--paper);
}

.knowledge-item p:not(.item-label) {
  min-height: 70px;
  margin-bottom: 22px;
  color: #acb8b4;
  font-size: 12px;
}

.knowledge-item code {
  border-color: #46534f;
  background: #222e2b;
  color: #f5d77d;
}

.knowledge-link {
  color: #61cfb6;
  font-size: 10px;
  font-weight: 700;
  text-decoration: none;
}

.knowledge-item-featured {
  box-shadow: inset 0 4px var(--coral);
}

.knowledge-item:nth-child(3) {
  box-shadow: inset 0 4px var(--teal);
}

.knowledge-item:nth-child(5) {
  box-shadow: inset 0 4px var(--yellow);
}

.misconception-list {
  border-top: 2px solid var(--ink);
}

.misconception-item {
  border-bottom: 1px solid var(--line-strong);
  background: var(--paper);
}

.misconception-item summary {
  display: grid;
  min-height: 70px;
  grid-template-columns: 44px minmax(0, 1fr) 28px;
  gap: 12px;
  align-items: center;
  padding: 12px 18px;
  color: var(--ink);
  font-size: 14px;
  font-weight: 700;
  list-style: none;
}

.misconception-item summary::-webkit-details-marker {
  display: none;
}

.misconception-item summary:hover {
  background: var(--page);
}

.summary-number {
  color: var(--coral-dark);
  font-size: 11px;
}

.summary-toggle {
  display: grid;
  width: 26px;
  height: 26px;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  color: var(--teal-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 17px;
}

.misconception-item[open] .summary-toggle {
  transform: rotate(45deg);
  background: var(--teal);
  color: var(--paper);
}

.misconception-item > p {
  margin: 0;
  padding: 0 74px 22px;
  color: var(--muted);
  font-size: 13px;
}

.quiz-score {
  flex: 0 0 auto;
  padding: 8px 13px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--paper);
  line-height: 1.15;
}

.quiz-score span {
  display: block;
  color: var(--muted);
  font-size: 9px;
}

.quiz-score strong {
  font-family: Consolas, "Courier New", monospace;
  font-size: 15px;
}

.quiz-form {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  border-top: 2px solid var(--ink);
  border-left: 1px solid var(--line);
}

.quiz-item {
  min-width: 0;
  margin: 0;
  padding: 22px;
  border: 0;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}

.quiz-item legend {
  width: 100%;
  min-height: 52px;
  padding: 0;
  color: var(--ink);
  font-size: 14px;
  font-weight: 700;
}

.question-number {
  display: inline-block;
  min-width: 32px;
  margin-right: 5px;
  color: var(--coral-dark);
  font-size: 10px;
}

.quiz-options {
  display: grid;
  gap: 6px;
}

.quiz-options label {
  position: relative;
  display: grid;
  min-height: 42px;
  grid-template-columns: 27px minmax(0, 1fr);
  gap: 9px;
  align-items: center;
  padding: 7px 9px;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  color: var(--ink-soft);
  font-size: 11px;
  cursor: pointer;
}

.quiz-options label:hover {
  border-color: var(--line-strong);
  background: var(--page);
}

.quiz-options input {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
}

.option-letter {
  display: grid;
  width: 25px;
  height: 25px;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
  font-weight: 700;
}

.quiz-options label:has(input:checked) {
  border-color: var(--teal);
  background: var(--teal-soft);
  color: var(--teal-dark);
}

.quiz-options input:checked + .option-letter {
  border-color: var(--teal);
  background: var(--teal);
  color: var(--paper);
}

.quiz-options label:has(input:focus-visible) {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

.quiz-feedback {
  min-height: 18px;
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 10px;
}

.quiz-feedback.is-correct {
  color: var(--teal-dark);
}

.quiz-feedback.is-incorrect {
  color: var(--coral-dark);
}

.quiz-actions {
  grid-column: 1 / -1;
  min-height: 72px;
  gap: 18px;
  padding: 14px 20px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: #e8ecea;
}

.primary-button {
  border-color: var(--ink);
  background: var(--ink);
  color: var(--paper);
}

.primary-button:hover {
  border-color: var(--coral-dark);
  background: var(--coral-dark);
}

.quiz-result {
  margin: 0 0 0 auto;
  color: var(--ink-soft);
  font-size: 12px;
  font-weight: 700;
}

.rigor-note {
  display: grid;
  grid-template-columns: 64px minmax(0, 1fr);
  gap: 24px;
  margin-block: 0 72px;
  padding: 26px 28px;
  border: 1px solid #ad942a;
  border-left: 5px solid var(--yellow);
  border-radius: var(--radius);
  background: var(--yellow-soft);
}

.rigor-symbol {
  display: grid;
  width: 54px;
  height: 54px;
  place-items: center;
  border: 1px solid #b9941e;
  border-radius: 50%;
  color: var(--yellow-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 22px;
}

.rigor-note .section-kicker {
  margin-bottom: 3px;
  color: #786620;
}

.rigor-note h2 {
  margin-bottom: 9px;
  font-size: 22px;
}

.rigor-note p {
  margin-bottom: 13px;
  color: #534a29;
  font-size: 12px;
}

.rigor-list {
  display: grid;
  gap: 5px;
  margin: 0;
  padding: 0;
  color: #615528;
  font-size: 10px;
  list-style: none;
}

.rigor-list span {
  margin-right: 7px;
  font-family: Consolas, "Courier New", monospace;
  font-weight: 700;
}

.site-footer {
  position: relative;
  z-index: 0;
  isolation: isolate;
  min-height: 64px;
  justify-content: space-between;
  padding-block: 16px;
  border-top: 1px solid #394541;
  color: #a7b3af;
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
}

.site-footer::before {
  position: absolute;
  z-index: -1;
  top: -1px;
  right: calc((100vw - 100%) / -2);
  bottom: 0;
  left: calc((100vw - 100%) / -2);
  background: var(--ink);
  content: "";
}

.noscript-message {
  position: fixed;
  z-index: 999;
  right: 16px;
  bottom: 16px;
  max-width: 420px;
  padding: 12px 16px;
  border: 1px solid #9f7d12;
  border-radius: var(--radius-sm);
  background: var(--yellow-soft);
  color: var(--ink);
  box-shadow: var(--shadow-tool);
  font-size: 12px;
}

button:disabled,
input:disabled {
  cursor: not-allowed;
  opacity: 0.48;
}

@media (max-width: 1180px) {
  .experiment-toolbar {
    grid-template-columns: 1fr auto;
  }

  .preset-group {
    grid-column: 1 / -1;
  }

  .experiment-grid {
    grid-template-columns: minmax(0, 1fr) 330px;
  }

  .visual-panel {
    padding: 16px;
  }

  .knowledge-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .knowledge-item {
    min-height: 240px;
  }
}

@media (max-width: 920px) {
  .topbar {
    gap: 20px;
  }

  .chapter-meta,
  .brand-rule {
    display: none;
  }

  .chapter-progress-wrap {
    width: min(240px, 38vw);
  }

  .intro-strip {
    grid-template-columns: 1fr;
    gap: 24px;
  }

  .intro-note {
    max-width: 620px;
  }

  .experiment-grid {
    grid-template-columns: 1fr;
  }

  .visual-panel {
    border-radius: 0;
  }

  .control-panel {
    border-top: 1px solid var(--line);
    border-left: 0;
    border-radius: 0 0 var(--radius) var(--radius);
  }

  .tab-panels {
    min-height: 0;
  }

  .tab-panel {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0 28px;
  }

  .tab-panel[hidden] {
    display: none !important;
  }

  .tab-panel > .panel-section {
    min-width: 0;
  }

  .tab-panel > .panel-section:nth-last-child(-n + 2) {
    border-bottom: 0;
  }

  .panel-footnote {
    clear: both;
  }

  .knowledge-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .quiz-form {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 700px) {
  html {
    scroll-padding-top: 66px;
  }

  .topbar {
    min-height: 60px;
    padding-inline: 16px;
  }

  .brand-code {
    display: none;
  }

  .brand-mark {
    width: 30px;
    height: 30px;
  }

  .brand-name {
    font-size: 18px;
  }

  .chapter-progress-wrap {
    width: 130px;
  }

  .progress-copy > span {
    display: none;
  }

  .progress-copy {
    justify-content: flex-end;
  }

  .intro-strip,
  .lab-section,
  .content-section,
  .rigor-note,
  .site-footer {
    width: min(calc(100% - 28px), var(--content));
  }

  .intro-strip {
    padding-block: 32px 28px;
  }

  h1 {
    font-size: 34px;
  }

  h2 {
    font-size: 25px;
  }

  .intro-lede {
    font-size: 16px;
  }

  .section-heading {
    align-items: flex-start;
    flex-direction: column;
    gap: 9px;
  }

  .section-description {
    max-width: none;
    text-align: left;
  }

  .experiment-toolbar {
    grid-template-columns: 1fr;
    gap: 16px;
    padding: 14px;
  }

  .preset-group,
  .view-group,
  .toolbar-actions {
    grid-column: 1;
  }

  .preset-button {
    flex: 1 1 calc(50% - 7px);
    justify-content: center;
  }

  .view-group,
  .view-group .segmented-control {
    width: 100%;
  }

  .toolbar-actions {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
  }

  .icon-button {
    width: 100%;
  }

  .visual-panel {
    padding: 12px;
  }

  .visual-header {
    min-height: 48px;
  }

  .canvas-hint {
    right: 9px;
    bottom: 9px;
    left: 9px;
    max-width: none;
  }

  .canvas-badge {
    top: 9px;
    right: 9px;
  }

  .visual-footer {
    align-items: flex-start;
    flex-direction: column;
    gap: 9px;
  }

  .canvas-readout {
    width: 100%;
    align-items: center;
    justify-content: space-between;
    flex-direction: row;
  }

  .tab-panel {
    display: block;
    padding-inline: 15px;
  }

  .panel-section {
    border-bottom: 1px solid var(--line) !important;
  }

  .panel-section:last-child {
    border-bottom: 0 !important;
  }

  .guided-grid,
  .knowledge-grid,
  .quiz-form {
    grid-template-columns: 1fr;
  }

  .guided-item {
    min-height: 210px;
    grid-template-columns: 34px minmax(0, 1fr) 54px;
    gap: 10px;
    padding: 18px 14px;
  }

  .item-symbol {
    width: 50px;
    height: 50px;
    font-size: 17px;
  }

  .knowledge-section {
    width: 100%;
    padding-inline: 14px;
  }

  .knowledge-item {
    min-height: 0;
  }

  .knowledge-number {
    margin-bottom: 22px;
  }

  .knowledge-item p:not(.item-label) {
    min-height: 0;
  }

  .misconception-item summary {
    grid-template-columns: 30px minmax(0, 1fr) 26px;
    padding-inline: 12px;
    font-size: 13px;
  }

  .misconception-item > p {
    padding: 0 42px 20px;
  }

  .quiz-item {
    padding: 18px 14px;
  }

  .quiz-actions {
    align-items: stretch;
    flex-direction: column;
    gap: 10px;
  }

  .quiz-actions .primary-button,
  .quiz-actions .text-button {
    width: 100%;
  }

  .quiz-result {
    margin-left: 0;
    text-align: center;
  }

  .rigor-note {
    grid-template-columns: 1fr;
    gap: 14px;
    padding: 20px;
  }

  .rigor-symbol {
    width: 42px;
    height: 42px;
  }

  .site-footer {
    min-height: 82px;
    align-items: flex-start;
    flex-direction: column;
    justify-content: center;
    gap: 2px;
  }

  .site-footer::before {
    height: 82px;
  }
}

@media (max-width: 430px) {
  .chapter-progress-wrap {
    width: 92px;
  }

  .intro-note {
    grid-template-columns: 1fr;
    padding-left: 14px;
  }

  .note-symbol {
    display: none;
  }

  .preset-button {
    flex-basis: 100%;
  }

  .canvas-badge {
    display: none;
  }

  .canvas-hint {
    font-size: 9px;
  }

  .check-grid {
    grid-template-columns: 1fr;
  }

  .radio-grid {
    gap: 5px;
  }

  .radio-row {
    padding-inline: 5px;
  }

  .guided-item {
    grid-template-columns: 28px minmax(0, 1fr);
  }

  .item-symbol {
    display: none;
  }

  .quiz-score {
    align-self: flex-start;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }

  #animation-toggle:checked + .check-mark::before {
    content: none;
  }
}

@media (forced-colors: active) {
  * {
    forced-color-adjust: auto;
  }

  .canvas-stage,
  .visual-panel,
  .experiment-toolbar,
  .knowledge-section {
    border: 1px solid CanvasText;
  }

  .legend-line-equipotential {
    border-top-style: dashed;
  }

  .swatch-positive {
    border-radius: 0;
  }

  .swatch-negative {
    transform: rotate(45deg);
  }
}

/* 推导与模型说明 */
.model-scope {
  display: grid;
  grid-template-columns: 120px minmax(0, 1fr);
  gap: 20px;
  align-items: start;
  margin: 0 0 22px;
  padding: 18px 20px;
  border: 1px solid #b7cdbf;
  border-left: 4px solid var(--teal);
  border-radius: var(--radius-sm);
  background: var(--teal-soft);
}

.model-scope strong {
  color: var(--teal-dark);
  font-size: 13px;
}

.model-scope p {
  margin: 0;
  color: var(--ink-soft);
  font-size: 13px;
}

.derivation-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  border-top: 2px solid var(--ink);
  border-left: 1px solid var(--line);
}

.derivation-item {
  min-width: 0;
  min-height: 300px;
  padding: 24px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}

.derivation-item-accent {
  background: #fff9e8;
  box-shadow: inset 0 4px var(--yellow);
}

.derivation-index {
  display: block;
  margin-bottom: 28px;
  color: var(--coral-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 10px;
  font-weight: 700;
}

.derivation-item h3 {
  margin-bottom: 14px;
}

.derivation-item p {
  margin-bottom: 11px;
  color: var(--muted);
  font-size: 12px;
}

.derivation-item p:last-child {
  margin-bottom: 0;
}

.equation {
  display: flex;
  min-height: 62px;
  align-items: center;
  justify-content: center;
  margin: 0 0 15px;
  padding: 12px 10px;
  border-block: 1px solid var(--line);
  background: var(--page);
  color: var(--ink);
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(17px, 2vw, 23px);
  font-style: italic;
  text-align: center;
}

.equation-stack {
  min-height: 112px;
  align-items: stretch;
  flex-direction: column;
  gap: 5px;
  font-size: clamp(14px, 1.7vw, 19px);
}

.equation-stack span {
  display: block;
}

.formula-detail {
  color: var(--teal-dark) !important;
  font-size: 10px !important;
}

.principle-table-wrap {
  margin-top: 24px;
  overflow-x: auto;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--paper);
}

.principle-table {
  width: 100%;
  min-width: 680px;
  border-collapse: collapse;
  font-size: 12px;
}

.principle-table caption {
  padding: 13px 16px;
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  font-weight: 750;
  text-align: left;
}

.principle-table th,
.principle-table td {
  padding: 11px 14px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.principle-table tr:last-child th,
.principle-table tr:last-child td {
  border-bottom: 0;
}

.principle-table th:last-child,
.principle-table td:last-child {
  border-right: 0;
}

.principle-table thead th {
  background: var(--page);
  color: var(--muted);
  font-size: 10px;
  text-transform: uppercase;
}

.principle-table tbody th {
  width: 125px;
  color: var(--coral-dark);
  white-space: nowrap;
}

.principle-table tbody td {
  color: var(--muted);
}

.visual-integrity {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin-top: 24px;
  border-top: 1px solid var(--line-strong);
  border-left: 1px solid var(--line);
}

.visual-integrity > div {
  min-height: 150px;
  padding: 16px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: #f8faf8;
}

.visual-integrity strong {
  display: block;
  margin-bottom: 8px;
  color: var(--ink);
  font-size: 13px;
}

.visual-integrity p {
  margin: 0;
  color: var(--muted);
  font-size: 11px;
}

.guided-item.is-complete {
  box-shadow: inset 4px 0 var(--teal);
  background: #f2faf7;
}

/* 帮助与导出对话框 */
.lab-dialog {
  width: min(620px, calc(100% - 28px));
  max-height: min(760px, calc(100vh - 28px));
  padding: 0;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--paper);
  color: var(--ink);
  box-shadow: 0 28px 90px rgb(23 32 31 / 25%);
}

.lab-dialog::backdrop {
  background: rgb(23 32 31 / 62%);
  backdrop-filter: blur(4px);
}

.dialog-shell {
  display: grid;
  max-height: inherit;
  grid-template-rows: auto minmax(0, 1fr) auto;
}

.dialog-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 20px;
  padding: 22px 24px 17px;
  border-bottom: 1px solid var(--line);
}

.dialog-header h2 {
  margin: 0;
  font-size: 24px;
}

.dialog-header .panel-kicker {
  color: var(--teal-dark);
}

.dialog-close {
  display: grid;
  width: 34px;
  height: 34px;
  flex: 0 0 auto;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  background: var(--paper);
  color: var(--ink);
  font-size: 23px;
  line-height: 1;
}

.dialog-close:hover {
  border-color: var(--coral);
  background: var(--coral-soft);
  color: var(--coral-dark);
}

.dialog-body {
  overflow-y: auto;
  padding: 20px 24px;
}

.help-steps {
  display: grid;
  gap: 0;
  margin: 0;
  padding: 0;
  list-style: none;
}

.help-steps li {
  display: grid;
  grid-template-columns: 36px minmax(0, 1fr);
  gap: 13px;
  padding: 13px 0;
  border-bottom: 1px solid var(--line);
}

.help-steps li > span {
  color: var(--coral-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 11px;
  font-weight: 700;
}

.help-steps strong {
  display: block;
  margin-bottom: 3px;
  font-size: 13px;
}

.help-steps p {
  margin: 0;
  color: var(--muted);
  font-size: 12px;
}

.dialog-note {
  margin-top: 17px;
  padding: 12px 14px;
  border-left: 3px solid var(--yellow);
  background: var(--yellow-soft);
}

.dialog-note strong {
  display: block;
  margin-bottom: 3px;
  color: var(--yellow-dark);
  font-size: 12px;
}

.dialog-note p,
.export-footnote {
  margin: 0;
  color: #615219;
  font-size: 11px;
}

.dialog-actions {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  padding: 14px 24px;
  border-top: 1px solid var(--line);
  background: var(--page);
}

.dialog-actions .primary-button,
.dialog-actions .outline-button {
  min-width: 100px;
  margin: 0;
}

.export-options {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.export-options button {
  display: grid;
  min-height: 150px;
  align-content: center;
  gap: 5px;
  padding: 18px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--paper);
  color: var(--ink);
  text-align: left;
}

.export-options button:hover {
  border-color: var(--teal);
  background: var(--teal-soft);
}

.export-icon {
  color: var(--coral-dark);
  font-family: Consolas, "Courier New", monospace;
  font-size: 24px;
}

.export-options strong {
  font-size: 13px;
}

.export-options small {
  color: var(--muted);
  font-size: 10px;
}

.export-footnote {
  margin-top: 16px;
  color: var(--muted);
}

@media (max-width: 920px) {
  .visual-integrity {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 700px) {
  .model-scope {
    grid-template-columns: 1fr;
    gap: 4px;
    padding: 15px;
  }

  .derivation-grid {
    grid-template-columns: 1fr;
  }

  .derivation-item {
    min-height: 0;
    padding: 19px 15px;
  }

  .derivation-index {
    margin-bottom: 18px;
  }

  .visual-integrity {
    grid-template-columns: 1fr;
  }

  .visual-integrity > div {
    min-height: 0;
  }

  .dialog-header,
  .dialog-body,
  .dialog-actions {
    padding-right: 16px;
    padding-left: 16px;
  }

  .dialog-header h2 {
    font-size: 21px;
  }

  .export-options {
    grid-template-columns: 1fr;
  }
}

@media print {
  :root {
    --page: #ffffff;
    --paper: #ffffff;
    --ink: #000000;
    --ink-soft: #222222;
    --muted: #4a4a4a;
    --line: #c4c4c4;
    --line-strong: #888888;
  }

  @page {
    size: A4 portrait;
    margin: 14mm;
  }

  html,
  body {
    background: #ffffff;
    color: #000000;
    font-size: 10pt;
  }

  .topbar {
    position: static;
    min-height: 48px;
    padding: 8px 0;
    border-color: #000000;
    background: #ffffff;
    color: #000000;
  }

  .brand,
  .brand-mark,
  .progress-copy strong {
    color: #000000;
  }

  .brand-mark {
    border-color: #000000;
  }

  .chapter-meta .eyebrow,
  .progress-copy {
    color: #444444;
  }

  .experiment-toolbar,
  .control-panel,
  .quiz-actions,
  .site-footer,
  .knowledge-section {
    background: #ffffff !important;
    color: #000000 !important;
  }

  .toolbar-actions,
  .preset-group,
  .view-group,
  .panel-tabs,
  .panel-footnote,
  .canvas-hint,
  .canvas-badge,
  .link-button,
  .knowledge-link,
  .quiz-actions,
  .noscript-message {
    display: none !important;
  }

  .experiment-toolbar {
    min-height: 14px;
    padding: 0;
    border: 1px solid #000000;
  }

  .experiment-grid {
    display: block;
    border-color: #000000;
    box-shadow: none;
  }

  .visual-panel {
    border-radius: 0;
    background: #ffffff;
    color: #000000;
  }

  .canvas-stage {
    border-color: #000000;
    background: #ffffff;
    print-color-adjust: exact;
  }

  .visual-header h3,
  .knowledge-item h3,
  .formula-block,
  .knowledge-item code {
    color: #000000;
  }

  .legend-item,
  .visual-caption,
  .knowledge-item p:not(.item-label),
  .knowledge-section .section-kicker,
  .knowledge-section .section-description {
    color: #333333;
  }

  .control-panel {
    border: 1px solid #000000;
  }

  .tab-panel {
    display: block !important;
    padding: 0 14px;
  }

  .tab-panel[hidden] {
    display: block !important;
  }

  .check-row,
  .radio-row {
    min-height: 24px;
  }

  .content-section {
    padding-block: 28px;
  }

  .guided-grid,
  .knowledge-grid,
  .quiz-form {
    grid-template-columns: repeat(2, 1fr);
    break-inside: auto;
  }

  .guided-item,
  .knowledge-item,
  .quiz-item,
  .misconception-item,
  .rigor-note {
    break-inside: avoid;
    background: #ffffff;
  }

  .knowledge-section {
    padding-inline: 0;
  }

  .knowledge-grid,
  .knowledge-item {
    border-color: #777777;
  }

  .knowledge-item code {
    border-color: #999999;
    background: #ffffff;
  }

  .misconception-item > p {
    display: block;
  }

  .summary-toggle {
    display: none;
  }

  .rigor-note {
    border-color: #777777;
  }

  .site-footer {
    border-top: 1px solid #000000;
    color: #333333;
  }

  .site-footer::before {
    display: none;
  }
}