.surfaces-explorer {
  --surface-teal: #167f85;
  color: var(--ink, #20252b);
  font-family: var(--font-ui, system-ui, sans-serif);
  min-width: 0;
  width: 100%;
  letter-spacing: 0;
}
.surfaces-explorer *, .surfaces-explorer *::before, .surfaces-explorer *::after { box-sizing: border-box; letter-spacing: 0; }
.surfaces-heading { display: flex; align-items: baseline; justify-content: space-between; flex-wrap: wrap; gap: 6px 16px; margin-bottom: 14px; }
.surfaces-heading h2 { margin: 0; font-size: 22px; }
.surfaces-heading > span { color: var(--muted, #5b6577); font-size: 12px; }
.surfaces-form { display: grid; grid-template-columns: minmax(160px, 0.75fr) minmax(220px, 2fr) 92px 90px auto; align-items: end; gap: 10px; padding-bottom: 12px; }
.surfaces-field { display: grid; gap: 4px; min-width: 0; font-size: 12px; color: var(--muted, #5b6577); }
.surfaces-input { border: 1px solid var(--line-2, #bac4cb); border-radius: 4px; background: var(--surface, #fff); color: var(--ink, #20252b); width: 100%; min-width: 0; min-height: 40px; padding: 7px 9px; font: inherit; font-size: 14px; }
.surfaces-equation { font-family: var(--font-mono, ui-monospace, monospace); }
.surfaces-input[aria-invalid="true"] { border-color: var(--bad, #b43d30); }
.surfaces-button { display: inline-flex; align-items: center; justify-content: center; gap: 6px; min-height: 40px; padding: 8px 12px; border: 1px solid var(--line-2, #bac4cb); border-radius: 4px; background: var(--surface, #fff); color: var(--ink, #20252b); cursor: pointer; font: inherit; font-size: 13px; white-space: nowrap; }
.surfaces-button:hover { background: var(--surface-2, #eef1f3); }
.surfaces-button:disabled { opacity: 0.5; cursor: not-allowed; }
.surfaces-button svg { width: 17px; height: 17px; flex: 0 0 auto; }
.surfaces-icon { width: 40px; height: 40px; padding: 4px; flex: 0 0 40px; }
.surfaces-render { border-color: var(--accent, #2a52c4); color: var(--accent, #2a52c4); }
.surfaces-toolbar { display: flex; flex-wrap: wrap; align-items: center; gap: 10px 18px; padding: 10px 0; border-top: 1px solid var(--line, #d6dce7); border-bottom: 1px solid var(--line, #d6dce7); }
.surfaces-check { display: inline-flex; gap: 6px; align-items: center; min-height: 32px; font-size: 13px; white-space: nowrap; }
.surfaces-check input { accent-color: var(--accent, #2a52c4); width: 16px; height: 16px; margin: 0; }
.surfaces-modes { display: inline-flex; min-width: 0; margin: 0; border: 0; padding: 0; }
.surfaces-modes label { position: relative; }
.surfaces-modes input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.surfaces-modes span { display: flex; align-items: center; justify-content: center; min-height: 36px; padding: 6px 12px; border: 1px solid var(--line-2, #bac4cb); background: var(--surface, #fff); cursor: pointer; font-size: 13px; }
.surfaces-modes label:first-of-type span { border-radius: 4px 0 0 4px; }
.surfaces-modes label:last-of-type span { border-radius: 0 4px 4px 0; border-left: 0; }
.surfaces-modes input:checked + span { color: var(--accent, #2a52c4); background: var(--accent-soft, #e3e9fb); }
.surfaces-modes input:focus-visible + span { outline: 2px solid var(--focus, #2a52c4); outline-offset: 2px; z-index: 1; position: relative; }
.surfaces-camera { display: flex; gap: 6px; margin-left: auto; min-width: 0; }
.surfaces-camera select { width: 134px; font-size: 13px; }
.surfaces-viewport { position: relative; width: 100%; height: max(400px, min(66dvh, 720px)); overflow: hidden; background: var(--surface, #fff); }
.surfaces-viewport canvas { display: block; width: 100%; height: 100%; touch-action: none; }
.surfaces-viewport canvas:focus-visible { outline: 2px solid var(--focus, #2a52c4); outline-offset: -3px; }
.surfaces-axis-label { position: absolute; transform: translate(-50%, -50%); pointer-events: none; font: 600 13px/1 var(--font-mono, monospace); text-shadow: 0 1px 3px var(--surface, #fff); }
.surfaces-axis-x { color: #ca5165; }
.surfaces-axis-y { color: #4c9161; }
.surfaces-axis-z { color: #527cc8; }
.surfaces-readout { display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between; gap: 3px 12px; border-top: 1px solid var(--line, #d6dce7); padding: 8px 0 4px; font-size: 12px; color: var(--muted, #5b6577); font-variant-numeric: tabular-nums; }
.surfaces-computation { display: flex; align-items: center; flex-wrap: wrap; gap: 6px 12px; min-height: 24px; }
.surfaces-status { margin: 0; font-size: 12px; color: var(--muted, #5b6577); overflow-wrap: anywhere; }
.surfaces-status[data-state="error"] { color: var(--bad, #b43d30); }
.surfaces-progress { width: 90px; height: 5px; accent-color: var(--surface-teal); }
.surfaces-example-note { margin: 8px 0 0; font-size: 13px; color: var(--ink-2, #333c4d); max-width: 100ch; overflow-wrap: anywhere; }
.surfaces-example-note:empty { display: none; }
.surfaces-example-book { margin: 4px 0 0; font-size: 12px; color: var(--muted, #5b6474); max-width: 100ch; overflow-wrap: anywhere; }
.surfaces-example-book:empty { display: none; }
.surfaces-numerical { margin: 7px 0 0; color: var(--muted, #5b6577); font-size: 12px; max-width: 110ch; overflow-wrap: anywhere; }
.surfaces-sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
.surfaces-explorer [hidden] { display: none !important; }
.surfaces-pair-controls { display:grid; grid-template-columns:minmax(0,2fr) minmax(190px,1fr) minmax(180px,1fr); gap:10px; padding-bottom:12px; }
.surfaces-chart-controls { display:grid; grid-template-columns:180px 110px minmax(0,1fr); align-items:center; gap:12px; padding-bottom:12px; }
.surfaces-chart-note { font-size:12px; line-height:1.5; color:var(--muted); margin:0; overflow-wrap:anywhere; }
.surfaces-workspace { display:grid; grid-template-columns:minmax(0,1fr) 330px; gap:20px; align-items:start; }
.surfaces-drawing { position:sticky; top:108px; min-width:0; }
.surfaces-analysis { min-width:0; padding-top:12px; }
.surfaces-analysis h3 { font-size:17px; }
.surfaces-tool, .surfaces-algebra { padding:12px 0; border-bottom:1px solid var(--line); display:flex; flex-direction:column; gap:9px; }
.surfaces-tool:last-child { border-bottom:0; }
.surfaces-tool p, .surfaces-algebra p { font-size:12.5px; line-height:1.5; }
.surfaces-math { max-width:100%; overflow:auto; font-size:14px; }
.surfaces-tool-row { display:flex; flex-wrap:wrap; align-items:center; gap:6px 12px; }
.surfaces-tool-row h3 { margin-right:auto; }
.surfaces-point-form { display:grid; grid-template-columns:minmax(0,1fr) 40px 40px; align-items:end; gap:6px; }
.surfaces-point-info { display:flex; flex-direction:column; gap:7px; }
.surfaces-tool-error { color:var(--bad); font-size:12px; overflow-wrap:anywhere; }
.surfaces-tool-error:empty { display:none; }
.surfaces-section-controls { display:grid; grid-template-columns:minmax(0,1fr) 100px; gap:8px; }
.surfaces-slice-slider { width:100%; accent-color:#bd4268; }
.surfaces-slice-canvas { width:100%; aspect-ratio:18/13; background:var(--surface); }
.surfaces-slice-canvas[aria-label^="Projective"] { aspect-ratio:12/11; }
.surfaces-analysis .surfaces-button { white-space:normal; }
.surfaces-legend { display:flex; flex-wrap:wrap; gap:14px; font-size:12px; padding-top:8px; }
.surfaces-legend span::before { content:''; display:inline-block; width:14px; height:3px; margin-right:5px; vertical-align:middle; background:currentColor; }
.surfaces-key-s { color:#218b91; }.surfaces-key-t { color:#8063b4; }.surfaces-key-intersection { color:#c45824; }
.surfaces-intersection-status, .surfaces-pair-degree { font-size:12px; line-height:1.5; margin-top:6px; }
.surfaces-intersection-status:empty, .surfaces-pair-degree:empty { display:none; }
.surfaces-analysis details { font-size:12px; }
.surfaces-analysis summary, .surfaces-pair-degree summary { cursor:pointer; }
/* Planes through a line (pencil mode of the section tool) */
.surfaces-key-line, .surfaces-key-residual { display:inline-flex; align-items:center; gap:5px; margin-right:10px; }
/* The swatches carry the drawn colours (surface-tools.mjs); the labels keep the text colour, readable in both themes. */
.surfaces-key-line::before, .surfaces-key-residual::before { content:''; display:inline-block; width:18px; height:0; border-top:2px solid #bd4268; }
.surfaces-key-line::before { border-top:2px dashed #d3801c; }
/* The lab inside a Practice question (surface-question.js) */
.surface-question-launch { gap:6px 12px; align-items:center; margin:10px 0 2px; }
.surface-question-intro { display:grid; gap:4px; margin-bottom:12px; }
.surface-question-intro p { margin:0; max-width:92ch; font-size:14px; line-height:1.5; }
.surface-question-intro p.small { font-size:12.5px; }
.surface-question-dialog .dialog-body { padding-top:14px; }
.surfaces-explorer.is-question .surfaces-heading { margin-bottom:8px; }
.surfaces-explorer.is-question .surfaces-form { grid-template-columns:minmax(220px, 1fr) 92px 90px auto; }
.surfaces-explorer.is-question .surfaces-equation[readonly] { background:var(--surface-2, #eef1f3); color:var(--ink-2, #333c4d); }
.surfaces-explorer.is-question .surfaces-drawing { top:0; }
.surfaces-explorer.is-question .surfaces-viewport { height:max(340px, min(56dvh, 600px)); }
/* On a wide screen the chart menus share the equation's row, so the 3-D view is in sight when the lab opens. */
@media (min-width: 1001px) {
  .surface-question-intro p { max-width:124ch; }
  .surfaces-explorer.is-question { display:grid; grid-template-columns:minmax(0,1fr) 150px 96px; column-gap:10px; }
  .surfaces-explorer.is-question > :not(.surfaces-form):not(.surfaces-chart-controls) { grid-column:1/-1; }
  .surfaces-explorer.is-question .surfaces-chart-controls { display:contents; }
  .surfaces-explorer.is-question .surfaces-chart-controls > .surfaces-field { align-self:end; padding-bottom:12px; }
  .surfaces-explorer.is-question .surfaces-chart-note { grid-column:1/-1; margin:-4px 0 10px; }
  .surfaces-explorer.is-question .surfaces-viewport { height:max(340px, min(calc(100dvh - 450px), 600px)); }
}
@media (max-width: 1000px) {
  .surfaces-chart-controls { grid-template-columns:180px 110px; }
  .surfaces-chart-note { grid-column:1/-1; }
  .surfaces-workspace { grid-template-columns:minmax(0,1fr); }
  .surfaces-drawing { position:static; }
  .surfaces-analysis { display:grid; grid-template-columns:repeat(2,minmax(0,1fr)); gap:0 20px; }
  .surfaces-form { grid-template-columns: minmax(140px, 1fr) minmax(100px, 1fr) minmax(90px, 1fr) auto; }
  .surfaces-equation-field { grid-column: 1 / -1; grid-row: 1; }
  .surfaces-explorer.is-question .surfaces-form { grid-template-columns:minmax(90px, 1fr) minmax(90px, 1fr) auto; }
  .surfaces-explorer.is-question .surfaces-chart-controls { grid-template-columns:180px 110px minmax(0,1fr); }
  .surfaces-explorer.is-question .surfaces-chart-note { grid-column:auto; }
}
@media (max-width: 560px) {
  .surfaces-analysis, .surfaces-pair-controls { grid-template-columns:minmax(0,1fr); }
  .surfaces-chart-controls { grid-template-columns:minmax(0,1fr) 100px; }
  .surfaces-form { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 8px; }
  .surfaces-preset-field { grid-column: 1 / -1; }
  .surfaces-render { grid-column: 1 / -1; min-height: 40px; }
  .surfaces-toolbar { gap: 6px 12px; }
  .surfaces-camera { width: 100%; margin-left: 0; }
  .surfaces-camera select { flex: 1; width: auto; }
  .surfaces-viewport { height: 440px; height: max(360px, min(58dvh, 500px)); }
  .surfaces-input { font-size: 16px; }
  .surfaces-check { font-size: 12px; }
  .surfaces-modes span { padding: 6px 10px; }
  .surfaces-heading > span { font-size: 11px; }
  /* On a phone the lab takes the whole screen; window, cells and Render share one row. */
  .overlay.surface-question-overlay { padding:0; }
  .dialog.surface-question-dialog { width:100% !important; height:100dvh; max-height:100dvh; border-radius:0; border:0; }
  .surface-question-dialog .dialog-head { padding:10px 12px 10px 16px; padding-top:calc(10px + env(safe-area-inset-top, 0px)); }
  .surface-question-dialog .dialog-head h3 { font-size:16px; }
  .surface-question-dialog .dialog-body { padding:12px 16px; flex:1 1 auto; }
  .surface-question-dialog .dialog-foot { padding:10px 16px calc(10px + env(safe-area-inset-bottom, 0px)); }
  .surface-question-intro { margin-bottom:10px; }
  .surfaces-explorer.is-question .surfaces-form { grid-template-columns:minmax(0, 1fr) minmax(0, 1fr) auto; }
  .surfaces-explorer.is-question .surfaces-render { grid-column:auto; }
  .surfaces-explorer.is-question .surfaces-viewport { height:max(320px, min(52dvh, 460px)); }
  /* The 3-D view comes right after its toolbar; the chart menus follow it, above the tools. */
  .surfaces-explorer.is-question { display:flex; flex-direction:column; }
  .surfaces-explorer.is-question .surfaces-heading { display:none; }
  .surfaces-explorer.is-question .surfaces-workspace { display:contents; }
  .surfaces-explorer.is-question .surfaces-chart-controls { order:1; margin-top:12px; padding-top:12px; border-top:1px solid var(--line, #d6dce7); grid-template-columns:minmax(0,1fr) 100px; }
  .surfaces-explorer.is-question .surfaces-chart-note { grid-column:1/-1; }
  .surfaces-explorer.is-question .surfaces-analysis { order:2; padding-top:0; }
}