:root {
  --ink: #172033;
  --ink-soft: #354054;
  --muted: #737c8b;
  --paper: #f7f4ed;
  --surface: #fffefb;
  --surface-muted: #f1eee6;
  --line: #dedbd2;
  --blue: #315efb;
  --blue-soft: #e8edff;
  --green: #159a7d;
  --green-soft: #dff3ed;
  --coral: #e76551;
  --coral-soft: #fbe8e3;
  --amber: #d89524;
  --amber-soft: #f8edd5;
  --teal-plane: #bfe3dc;
  --shadow: 0 16px 42px rgb(37 44 57 / 7%);
  --radius: 20px;
}

* {
  box-sizing: border-box;
}

html {
  color-scheme: light;
  background: var(--paper);
}

body {
  margin: 0;
  min-width: 320px;
  background:
    radial-gradient(circle at 8% 0%, rgb(49 94 251 / 6%), transparent 28rem),
    radial-gradient(circle at 92% 16%, rgb(21 154 125 / 6%), transparent 31rem),
    var(--paper);
  color: var(--ink);
  font-family: "DM Sans", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 15px;
  line-height: 1.5;
}

button,
input,
select {
  font: inherit;
}

button,
select,
input[type="range"] {
  accent-color: var(--blue);
}

button:focus-visible,
select:focus-visible,
input:focus-visible,
[tabindex="0"]:focus-visible {
  outline: 3px solid rgb(49 94 251 / 30%);
  outline-offset: 2px;
}

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

h1,
h2 {
  color: var(--ink);
}

h1 {
  margin-bottom: 0;
  font-family: "Newsreader", Georgia, serif;
  font-size: clamp(1.7rem, 2.4vw, 2.35rem);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.025em;
}

h2 {
  margin-bottom: 0;
  font-size: 1rem;
  line-height: 1.25;
}

.page-shell {
  width: min(1880px, 100%);
  margin: 0 auto;
  padding: 10px clamp(12px, 1.5vw, 24px) 18px;
}

.topbar {
  display: flex;
  align-items: center;
  min-height: 22px;
  margin-bottom: 6px;
}

.library-link {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  width: fit-content;
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 600;
  text-decoration: none;
}

.library-link:hover {
  color: var(--blue);
}

.title-block {
  text-align: center;
}

.eyebrow {
  margin-bottom: 3px;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.13em;
  line-height: 1.3;
  text-transform: uppercase;
}

.example-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 78px;
  align-items: end;
  gap: 6px 8px;
  padding: 10px 12px;
}

.example-card .section-heading {
  grid-column: 1 / -1;
}

.example-card .section-heading > div {
  display: flex;
  align-items: baseline;
  gap: 8px;
  min-width: 0;
}

.example-card .section-heading .eyebrow {
  margin: 0;
}

.example-card h2 {
  font-size: 0.92rem;
  white-space: nowrap;
}

.example-actions {
  display: grid;
  gap: 4px;
}

.example-card select {
  width: 100%;
  min-width: 0;
  min-height: 32px;
  padding-left: 9px;
  font-size: 0.72rem;
}

.example-card .quiet-button {
  min-height: 24px;
  padding: 0 5px;
  border-radius: 8px;
  font-size: 0.65rem;
}

.preset-field {
  display: grid;
  gap: 3px;
  color: var(--muted);
  font-size: 0.74rem;
  font-weight: 600;
}

select,
.quiet-button,
.icon-button,
.primary-button,
.text-button {
  border: 0;
  border-radius: 10px;
  cursor: pointer;
}

select,
.quiet-button {
  min-height: 38px;
  border: 1px solid var(--line);
  background: rgb(255 254 251 / 75%);
  color: var(--ink-soft);
}

select {
  padding: 0 34px 0 11px;
}

.quiet-button {
  padding: 0 13px;
  font-size: 0.76rem;
  font-weight: 600;
}

.quiet-button:hover,
select:hover {
  border-color: #c3c7ce;
  background: var(--surface);
}

.lesson-nav {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 6px;
  padding: 6px;
  margin-bottom: 12px;
  border: 1px solid rgb(222 219 210 / 80%);
  border-radius: 15px;
  background: rgb(255 254 251 / 52%);
}

.lesson-tab {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 42px;
  padding: 7px 10px;
  border: 0;
  border-radius: 10px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 600;
  transition: background 160ms ease, color 160ms ease, box-shadow 160ms ease;
}

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

.lesson-tab.is-active {
  background: var(--surface);
  box-shadow: 0 4px 16px rgb(39 48 66 / 8%);
  color: var(--ink);
}

.lesson-number {
  display: grid;
  width: 23px;
  height: 23px;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-muted);
  color: var(--muted);
  font-size: 0.68rem;
}

.lesson-tab.is-active .lesson-number {
  background: var(--blue);
  color: white;
}

.workspace {
  display: grid;
  grid-template-columns: minmax(238px, 0.72fr) minmax(500px, 1.8fr) minmax(325px, 1fr);
  grid-template-rows: 315px 420px;
  align-items: stretch;
  gap: 12px;
}

.left-column,
.visual-column,
.right-column {
  display: contents;
}

.left-top-stack,
.right-bottom-stack {
  display: grid;
  min-width: 0;
  min-height: 0;
  gap: 12px;
}

.left-top-stack {
  grid-column: 1;
  grid-row: 1;
  grid-template-rows: 102px minmax(0, 1fr);
}

.data-controls {
  grid-column: 1;
  grid-row: 2;
}

.plot-card {
  grid-column: 2;
  grid-row: 1;
}

.geometry-card {
  grid-column: 2;
  grid-row: 2;
}

.math-card {
  grid-column: 3;
  grid-row: 1;
}

.right-bottom-stack {
  grid-column: 3;
  grid-row: 2;
  grid-template-rows: 206px minmax(0, 1fr);
}

.card {
  min-width: 0;
  border: 1px solid rgb(222 219 210 / 88%);
  border-radius: var(--radius);
  background: rgb(255 254 251 / 92%);
  box-shadow: var(--shadow);
}

.lesson-card,
.data-controls,
.math-card,
.perturbation-card,
.identity-card {
  padding: 14px;
}

.lesson-card {
  min-height: 0;
  padding: 11px 14px;
  overflow: hidden;
  background:
    linear-gradient(145deg, rgb(49 94 251 / 6%), transparent 48%),
    var(--surface);
}

.step-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 5px;
  color: var(--blue);
  font-size: 0.62rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.step-rule {
  flex: 1;
  height: 1px;
  background: rgb(49 94 251 / 20%);
}

.lesson-card h2 {
  max-width: none;
  margin-bottom: 4px;
  font-family: "Newsreader", Georgia, serif;
  font-size: 1.08rem;
  font-weight: 600;
  line-height: 1.15;
  letter-spacing: -0.02em;
}

.lesson-card > p {
  margin-bottom: 5px;
  color: var(--ink-soft);
  font-size: 0.7rem;
  line-height: 1.35;
}

.step-insight {
  min-height: 0;
  padding: 5px 8px;
  border-left: 3px solid var(--blue);
  background: var(--blue-soft);
  color: #2b417f;
  font-size: 0.64rem;
  line-height: 1.35;
}

.step-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-top: 5px;
}

.lesson-card .primary-button {
  min-height: 30px;
  padding: 0 11px;
  font-size: 0.7rem;
}

.lesson-card .text-button {
  font-size: 0.7rem;
}

.primary-button {
  min-height: 38px;
  padding: 0 14px;
  background: var(--ink);
  color: white;
  font-size: 0.76rem;
  font-weight: 700;
}

.primary-button:hover {
  background: #28334a;
}

.primary-button:disabled,
.text-button:disabled {
  cursor: default;
  opacity: 0.35;
}

.text-button {
  padding: 6px 2px;
  background: transparent;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 600;
}

.text-button:hover:not(:disabled) {
  color: var(--blue);
}

.text-button.compact {
  padding: 4px 6px;
  font-size: 0.68rem;
}

.section-heading,
.visual-heading {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
}

.section-copy {
  margin: 10px 0 16px;
  color: var(--muted);
  font-size: 0.75rem;
}

.blue-text {
  color: var(--blue);
  font-weight: 700;
}

.mini-badge,
.rank-badge,
.status-dot {
  display: inline-flex;
  align-items: center;
  min-height: 24px;
  padding: 0 8px;
  border-radius: 999px;
  background: var(--surface-muted);
  color: var(--muted);
  font-size: 0.63rem;
  font-weight: 700;
  white-space: nowrap;
}

.rank-badge {
  background: var(--green-soft);
  color: #10725e;
}

.status-dot::before {
  width: 6px;
  height: 6px;
  margin-right: 6px;
  border-radius: 50%;
  background: var(--green);
  content: "";
}

.observation-controls {
  display: grid;
  gap: 13px;
}

.observation-control {
  --point-color: var(--blue);
  display: grid;
  position: relative;
  grid-template-columns: 26px 28px minmax(70px, 1fr) 58px;
  align-items: center;
  gap: 7px;
  border-radius: 9px;
  transition: background 140ms ease, box-shadow 140ms ease;
}

.observation-control.is-observation-highlighted {
  background: var(--blue-soft);
  box-shadow: 0 0 0 5px var(--blue-soft);
}

.observation-control.is-observation-highlighted .point-token {
  box-shadow: 0 0 0 4px rgb(49 94 251 / 16%);
}

.observation-2 {
  --point-color: #5579ef;
}

.observation-3 {
  --point-color: #7892e8;
}

.point-token {
  display: grid;
  width: 24px;
  height: 24px;
  place-items: center;
  border-radius: 50%;
  background: var(--point-color);
  color: white;
  font-size: 0.67rem;
  font-weight: 700;
}

.control-symbol {
  color: var(--ink-soft);
  font-family: "Newsreader", Georgia, serif;
  font-size: 0.9rem;
  font-style: italic;
}

.observation-control input[type="range"] {
  width: 100%;
  min-width: 0;
}

.number-input {
  width: 58px;
  height: 31px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: white;
  color: var(--ink);
  font-size: 0.72rem;
  font-variant-numeric: tabular-nums;
  text-align: center;
}

.design-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  padding-top: 14px;
  margin-top: 15px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.7rem;
  font-weight: 600;
}

.x-values {
  display: flex;
  gap: 5px;
}

.x-value {
  min-width: 32px;
  padding: 4px 6px;
  border-radius: 7px;
  background: var(--surface-muted);
  color: var(--ink-soft);
  font-variant-numeric: tabular-nums;
  text-align: center;
}

.geometry-card,
.plot-card {
  display: grid;
  grid-template-rows: auto minmax(0, 1fr) auto;
  height: 100%;
  overflow: hidden;
}

.visual-heading {
  padding: 12px 15px 0;
}

.math-serif {
  font-family: "Newsreader", Georgia, serif;
}

.geometry-tools {
  display: flex;
  align-items: center;
  gap: 7px;
}

.icon-button {
  display: grid;
  width: 30px;
  height: 30px;
  place-items: center;
  background: var(--surface-muted);
  color: var(--muted);
  font-size: 1rem;
}

.icon-button:hover {
  color: var(--blue);
}

.scene-container {
  position: relative;
  height: auto;
  min-height: 0;
  overflow: hidden;
  cursor: grab;
}

.scene-container:active {
  cursor: grabbing;
}

.scene-canvas,
.scene-label-layer {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.scene-label-layer {
  pointer-events: auto;
}

.scene-hint {
  position: absolute;
  z-index: 3;
  right: 14px;
  bottom: 10px;
  padding: 5px 8px;
  border: 1px solid rgb(222 219 210 / 70%);
  border-radius: 7px;
  background: rgb(255 254 251 / 75%);
  color: var(--muted);
  font-size: 0.62rem;
  pointer-events: none;
}

.coefficient-inset {
  position: absolute;
  z-index: 5;
  left: 12px;
  bottom: 10px;
  width: min(218px, calc(100% - 24px));
  padding: 8px 9px 7px;
  border: 1px solid rgb(222 219 210 / 88%);
  border-radius: 13px;
  background: rgb(255 254 251 / 92%);
  box-shadow: 0 10px 28px rgb(23 32 51 / 10%);
  opacity: 0;
  pointer-events: none;
  transform: translateY(5px);
  transition: opacity 160ms ease, transform 160ms ease, border-color 160ms ease;
}

.coefficient-inset.is-visible {
  opacity: 0.78;
  pointer-events: auto;
  transform: translateY(0);
}

.coefficient-inset.is-emphasized,
.coefficient-inset:focus-within,
.coefficient-inset:hover {
  border-color: rgb(49 94 251 / 25%);
  opacity: 1;
}

.coefficient-inset.is-dragging {
  cursor: grabbing;
  opacity: 1;
}

.coefficient-inset-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  color: var(--ink-soft);
  font-size: 0.66rem;
}

.coefficient-inset-heading strong {
  font-size: 0.68rem;
}

.coefficient-inset-badge {
  padding: 2px 6px;
  border-radius: 999px;
  background: var(--surface-muted);
  color: var(--muted);
  font-size: 0.56rem;
  font-weight: 700;
}

.coefficient-inset svg {
  display: block;
  width: 100%;
  height: 104px;
  margin-top: 2px;
  overflow: visible;
  font-family: "DM Sans", sans-serif;
}

.coefficient-inset-status {
  margin: 0;
  color: var(--muted);
  font-size: 0.57rem;
  font-weight: 600;
  text-align: center;
}

.coefficient-plot-background {
  fill: rgb(247 244 237 / 58%);
  stroke: rgb(222 219 210 / 80%);
}

.coefficient-grid {
  stroke: var(--line);
  stroke-width: 0.8;
}

.coefficient-axis {
  stroke: var(--muted);
  stroke-width: 1;
}

.coefficient-tick,
.coefficient-axis-label {
  fill: var(--muted);
  font-size: 7px;
}

.coefficient-axis-label {
  font-family: "Newsreader", Georgia, serif;
  font-size: 9px;
  font-style: italic;
  font-weight: 600;
}

.equivalent-coefficient-line {
  stroke: var(--green);
  stroke-width: 3;
  stroke-dasharray: 5 4;
  opacity: 0.65;
}

.coefficient-h-arrow {
  stroke: var(--amber);
  stroke-width: 2;
  stroke-dasharray: 4 3;
}

.coefficient-arrow-head {
  fill: var(--amber);
}

.optimal-coefficient-point {
  fill: var(--green);
  stroke: white;
  stroke-width: 2;
}

.candidate-coefficient-point {
  fill: var(--amber);
  stroke: white;
  stroke-width: 2.5;
  cursor: grab;
  outline: none;
  filter: drop-shadow(0 2px 3px rgb(216 149 36 / 30%));
  touch-action: none;
}

.candidate-coefficient-point:hover,
.candidate-coefficient-point:focus-visible {
  stroke: var(--ink);
  stroke-width: 2;
}

.optimal-coefficient-label,
.candidate-coefficient-label {
  font-family: "Newsreader", Georgia, serif;
  font-size: 10px;
  font-style: italic;
  font-weight: 600;
  pointer-events: none;
}

.optimal-coefficient-label { fill: var(--green); }
.candidate-coefficient-label { fill: var(--amber); }

.scene-label {
  display: inline-grid;
  min-width: 25px;
  height: 25px;
  padding: 0 6px;
  place-items: center;
  border: 1px solid rgb(255 255 255 / 72%);
  border-radius: 999px;
  box-shadow: 0 3px 10px rgb(23 32 51 / 12%);
  color: white;
  font-family: "Newsreader", Georgia, serif;
  font-size: 0.8rem;
  font-style: italic;
  font-weight: 600;
  pointer-events: none;
  white-space: nowrap;
}

.data-label { background: var(--blue); }
.fit-label { background: var(--green); }
.residual-label { background: var(--coral); }
.candidate-label { background: var(--amber); }
.coordinate-highlight-label {
  background: var(--blue);
  animation: observation-pulse 900ms ease-in-out infinite;
}

.axis-label,
.origin-label,
.basis-label,
.plane-label {
  min-width: 0;
  height: auto;
  border: 0;
  border-radius: 0;
  background: transparent;
  box-shadow: none;
  color: var(--muted);
  font-family: "DM Sans", sans-serif;
  font-size: 0.68rem;
  font-style: normal;
}

.scene-label.axis-label.is-observation-highlighted {
  padding: 3px 6px;
  border-radius: 999px;
  background: var(--blue-soft);
  box-shadow: 0 0 0 1px rgb(49 94 251 / 18%);
  color: var(--blue);
  font-weight: 700;
  animation: observation-pulse 900ms ease-in-out infinite;
}

@keyframes observation-pulse {
  0%, 100% { box-shadow: 0 0 0 1px rgb(49 94 251 / 18%); }
  50% { box-shadow: 0 0 0 7px rgb(49 94 251 / 10%); }
}

.basis-label {
  color: var(--green);
  font-family: "Newsreader", Georgia, serif;
  font-size: 0.82rem;
  font-style: italic;
}

.plane-label {
  padding: 4px 7px;
  border: 1px solid rgb(21 154 125 / 18%);
  border-radius: 7px;
  background: rgb(255 254 251 / 70%);
  color: #167863;
  font-weight: 700;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 12px;
  padding: 8px 14px 12px;
  border-top: 1px solid rgb(222 219 210 / 60%);
  color: var(--muted);
  font-size: 0.65rem;
}

.legend span {
  display: inline-flex;
  align-items: center;
  gap: 5px;
}

.legend b {
  color: var(--ink-soft);
  font-family: "Newsreader", Georgia, serif;
  font-size: 0.76rem;
  font-style: italic;
}

.legend-mark {
  width: 14px;
  height: 3px;
  border-radius: 999px;
}

.mark-data { background: var(--blue); }
.mark-fit { background: var(--green); }
.mark-residual { background: var(--coral); }
.mark-candidate { background: var(--amber); }

.drag-note {
  margin: 4px 0 0;
  color: var(--muted);
  font-size: 0.64rem;
}

.data-plot {
  min-height: 0;
  padding: 0 10px;
  overflow: hidden;
}

.data-plot svg {
  width: 100% !important;
  height: 100% !important;
}

.least-squares-data-plot .observed-point:hover .observed-point-marker,
.least-squares-data-plot .observed-point.is-dragging .observed-point-marker,
.least-squares-data-plot .observed-point.is-observation-highlighted .observed-point-marker {
  filter: brightness(1.08) drop-shadow(0 0 5px rgb(49 94 251 / 38%));
}

.least-squares-data-plot .observed-point.is-observation-highlighted .point-focus-ring {
  opacity: 1 !important;
}

.plot-caption {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 14px;
  padding: 0 14px 9px;
  color: var(--muted);
  font-size: 0.63rem;
}

.plot-caption span {
  display: inline-flex;
  align-items: center;
  gap: 5px;
}

.line-key {
  display: inline-block;
  width: 18px;
  border-top: 3px solid;
}

.fit-line-key { border-color: var(--green); }
.residual-line-key { border-color: var(--coral); }
.candidate-line-key { border-color: var(--amber); border-top-style: dashed; }

.math-card,
.perturbation-card,
.identity-card {
  height: 100%;
  overflow: hidden;
}

.math-card {
  display: flex;
  flex-direction: column;
}

.math-chain {
  display: grid;
  flex: 1;
  gap: 4px;
  min-height: 0;
  margin-top: 9px;
}

.math-row {
  position: relative;
  padding: 6px 9px;
  border: 1px solid transparent;
  border-radius: 11px;
  background: rgb(241 238 230 / 45%);
  opacity: 0.65;
  transition: opacity 160ms ease, border-color 160ms ease, background 160ms ease;
}

.math-row:not(.is-active) .math-display,
.math-row:not(.is-active) .zero-checks {
  display: none;
}

.math-row.is-active {
  border-color: rgb(49 94 251 / 18%);
  background: var(--blue-soft);
  opacity: 1;
}

.math-row-label {
  display: block;
  margin-bottom: 2px;
  color: var(--muted);
  font-size: 0.58rem;
  font-weight: 700;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.math-display {
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
  color: var(--ink);
}

.math-display .katex-display,
.identity-equation .katex-display {
  margin: 0.25em 0;
  text-align: left;
}

.math-display .katex {
  font-size: 0.78em;
}

.math-row[data-math-step="2"] .katex,
.math-row[data-math-step="3"] .katex {
  font-size: 0.71em;
}

.zero-checks {
  display: grid;
  gap: 2px;
  margin-top: 5px;
  color: var(--green);
}

.zero-checks .katex {
  font-size: 0.7em;
}

.perturbation-card {
  border-color: rgb(216 149 36 / 23%);
  background:
    linear-gradient(145deg, rgb(216 149 36 / 6%), transparent 50%),
    var(--surface);
}

.compact-math {
  margin: 3px 0;
}

.perturbation-card,
.identity-card {
  padding: 12px 14px;
}

.perturbation-card .compact-math .katex {
  font-size: 0.72em;
}

.future-card-placeholder {
  display: none;
}

.perturbation-card.is-locked .compact-math,
.perturbation-card.is-locked .h-control,
.perturbation-card.is-locked .section-heading .text-button,
.identity-card.is-locked .identity-equation,
.identity-card.is-locked .distance-bars,
.identity-card.is-locked .rank-note {
  display: none;
}

.perturbation-card.is-locked,
.identity-card.is-locked {
  border-color: rgb(222 219 210 / 88%);
  background:
    linear-gradient(145deg, rgb(115 124 139 / 4%), transparent 52%),
    var(--surface);
}

.is-locked .future-card-placeholder {
  display: grid;
  min-height: 112px;
  place-content: center;
  justify-items: center;
  gap: 8px;
  padding: 12px 14px;
  color: var(--muted);
  text-align: center;
}

.future-step-token {
  display: grid;
  width: 27px;
  height: 27px;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-muted);
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 700;
}

.future-card-placeholder p {
  max-width: 34ch;
  margin: 0;
  font-size: 0.66rem;
  line-height: 1.45;
}

.h-control {
  display: grid;
  grid-template-columns: 26px minmax(0, 1fr) 42px;
  align-items: center;
  gap: 7px;
  margin-top: 3px;
  color: var(--ink-soft);
  font-family: "Newsreader", Georgia, serif;
  font-style: italic;
}

.h-control input {
  min-width: 0;
}

.h-control output {
  color: var(--amber);
  font-family: "DM Sans", sans-serif;
  font-size: 0.7rem;
  font-style: normal;
  font-variant-numeric: tabular-nums;
  font-weight: 700;
  text-align: right;
}

.identity-card h2 {
  margin-bottom: 4px;
}

.identity-equation {
  overflow-x: auto;
  margin-bottom: 5px;
}

.identity-equation .katex {
  font-size: 0.72em;
}

.distance-bars {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr;
  align-items: end;
  gap: 6px;
}

.distance-label {
  display: grid;
  gap: 2px;
  margin-bottom: 3px;
  font-size: 0.55rem;
}

.distance-label span {
  color: var(--muted);
}

.distance-label strong {
  color: var(--ink);
  font-size: 0.77rem;
  font-variant-numeric: tabular-nums;
}

.bar-track {
  height: 7px;
  overflow: hidden;
  border-radius: 999px;
  background: var(--surface-muted);
}

.bar-track span {
  display: block;
  width: 0;
  height: 100%;
  border-radius: inherit;
  transition: width 180ms ease;
}

.candidate-distance .bar-track span { background: var(--ink-soft); }
.minimum-distance .bar-track span { background: var(--coral); }
.extra-distance .bar-track span { background: var(--amber); }

.distance-operation {
  padding-bottom: 0;
  color: var(--muted);
  font-family: "Newsreader", Georgia, serif;
  font-size: 0.9rem;
}

.rank-note {
  padding: 5px 8px;
  margin: 6px 0 0;
  border-radius: 9px;
  background: var(--green-soft);
  color: #28675a;
  font-size: 0.62rem;
  line-height: 1.35;
}

.data-table-section {
  padding: 0 16px;
  margin-top: 10px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgb(255 254 251 / 72%);
}

.data-table-section summary {
  display: flex;
  min-height: 42px;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  cursor: pointer;
  list-style: none;
}

.data-table-section summary::-webkit-details-marker {
  display: none;
}

.data-table-section summary strong {
  display: block;
  color: var(--ink);
  font-size: 0.82rem;
}

.data-table-section[open] {
  padding-bottom: 12px;
}

.table-summary-hint {
  color: var(--muted);
  font-size: 0.66rem;
  font-weight: 600;
}

.table-wrap {
  overflow-x: auto;
}

table {
  width: 100%;
  min-width: 520px;
  table-layout: fixed;
  border-collapse: collapse;
  color: var(--ink-soft);
  font-size: 0.73rem;
  font-variant-numeric: tabular-nums;
}

th,
td {
  padding: 6px 10px;
  overflow: hidden;
  border-bottom: 1px solid var(--line);
  font-variant-numeric: tabular-nums;
  text-align: right;
  text-overflow: ellipsis;
  white-space: nowrap;
}

th:first-child {
  text-align: left;
}

thead th:first-child {
  width: 32%;
}

thead th:not(:first-child) {
  width: 17%;
}

thead th {
  color: var(--muted);
  font-size: 0.62rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

tbody tr {
  transition: color 140ms ease;
}

tbody tr th,
tbody tr td {
  transition: background 140ms ease, box-shadow 140ms ease;
}

tbody tr.is-observation-highlighted {
  color: var(--blue);
}

tbody tr.is-observation-highlighted th,
tbody tr.is-observation-highlighted td {
  background: var(--blue-soft);
  font-weight: 700;
}

tbody tr.is-observation-highlighted th:first-child {
  box-shadow: inset 3px 0 0 var(--blue);
}

tbody tr:last-child th,
tbody tr:last-child td {
  border-bottom: 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;
}

body:not([data-lesson-step="1"]):not([data-lesson-step="4"]) #candidateLegend {
  opacity: 0.5;
}

@media (max-width: 1320px) {
  .workspace {
    grid-template-columns: minmax(220px, 0.72fr) minmax(450px, 1.6fr) minmax(290px, 0.9fr);
  }

  .page-shell {
    padding-inline: 10px;
  }

  .math-display .katex {
    font-size: 0.71em;
  }
}

@media (max-width: 1080px) {
  .workspace {
    grid-template-columns: minmax(230px, 0.7fr) minmax(0, 1.6fr);
    grid-template-rows: auto;
  }

  .left-column,
  .visual-column,
  .right-column {
    display: grid;
    min-width: 0;
    gap: 12px;
  }

  .left-column {
    grid-column: 1;
  }

  .visual-column {
    grid-column: 2;
  }

  .right-column {
    grid-column: 1 / -1;
    grid-template-columns: 1fr 1fr;
  }

  .left-top-stack,
  .right-bottom-stack,
  .data-controls,
  .plot-card,
  .geometry-card,
  .math-card {
    grid-column: auto;
    grid-row: auto;
  }

  .plot-card,
  .geometry-card,
  .math-card,
  .data-controls,
  .perturbation-card,
  .identity-card {
    height: auto;
  }

  .scene-container {
    height: 390px;
    min-height: 390px;
  }

  .data-plot svg {
    height: auto !important;
  }
}

@media (max-width: 780px) {
  .page-shell {
    padding: 8px 9px 24px;
  }

  .lesson-nav {
    overflow-x: auto;
    grid-template-columns: repeat(5, minmax(112px, 1fr));
    justify-content: start;
  }

  .workspace {
    display: flex;
    flex-direction: column;
  }

  .left-column,
  .visual-column,
  .right-column,
  .left-top-stack,
  .right-bottom-stack {
    display: contents;
  }

  .example-card { order: 1; }
  .lesson-card { order: 2; }
  .plot-card { order: 3; }
  .data-controls { order: 4; }
  .geometry-card { order: 5; }
  .math-card { order: 6; }
  .perturbation-card { order: 7; }
  .identity-card { order: 8; }

  .lesson-card h2 {
    max-width: none;
  }

  .scene-container {
    height: 370px;
    min-height: 370px;
  }

  .math-row:not(.is-active) .math-display,
  .math-row:not(.is-active) .zero-checks {
    display: block;
  }
}

@media (max-width: 480px) {
  .lesson-tab {
    justify-content: flex-start;
  }

  .library-link span:last-child {
    display: none;
  }

  .example-card {
    grid-template-columns: 1fr;
  }

  .example-card .section-heading {
    grid-column: auto;
  }

  .preset-field,
  .preset-field select {
    width: 100%;
    max-width: none;
  }

  .observation-control {
    grid-template-columns: 26px 24px minmax(60px, 1fr) 55px;
  }

  .scene-container {
    min-height: 330px;
    height: 330px;
  }

  .distance-bars {
    grid-template-columns: 1fr;
    align-items: stretch;
    gap: 8px;
  }

  .distance-operation {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}