:root {
  --bg: #f4f6f9;
  --panel-bg: #ffffff;
  --panel-border: #dfe4ea;
  --text: #1f2733;
  --text-muted: #5b6779;
  --accent: #2f6fed;
  --accent-soft: #e8effe;
  --grid-line: #eceff3;
  --axis-line: #b9c1cd;
  --shadow: 0 1px 3px rgba(20, 30, 50, 0.08), 0 1px 2px rgba(20, 30, 50, 0.06);
  --radius: 10px;
  font-size: 15px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12161d;
    --panel-bg: #1a2029;
    --panel-border: #2b3341;
    --text: #e7ebf1;
    --text-muted: #9aa5b4;
    --accent: #6c9bff;
    --accent-soft: #202c47;
    --grid-line: #232b37;
    --axis-line: #475364;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.4), 0 1px 2px rgba(0, 0, 0, 0.3);
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", "Helvetica Neue", Arial, sans-serif;
  line-height: 1.45;
}

.app-header {
  padding: 28px 32px 18px;
  max-width: 1200px;
  margin: 0 auto;
}

.app-header h1 {
  margin: 0 0 8px;
  font-size: 1.6rem;
  letter-spacing: -0.01em;
}

.subtitle {
  margin: 0;
  color: var(--text-muted);
  max-width: 72ch;
}

.app-layout {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 32px 32px;
  display: grid;
  grid-template-columns: minmax(0, 1.5fr) minmax(300px, 1fr);
  gap: 20px;
  align-items: start;
}

@media (max-width: 900px) {
  .app-layout {
    grid-template-columns: 1fr;
  }
}

.viz-column {
  display: flex;
  flex-direction: column;
  gap: 20px;
  min-width: 0;
}

.panel {
  background: var(--panel-bg);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 16px 18px 12px;
}

.panel h2 {
  margin: 0 0 10px;
  font-size: 1.02rem;
  font-weight: 600;
  color: var(--text);
}

.panel svg {
  width: 100%;
  height: auto;
  display: block;
}

.derived-list {
  display: grid;
  grid-template-columns: auto 1fr;
  column-gap: 14px;
  row-gap: 6px;
  margin: 0;
  font-size: 0.92rem;
}

.derived-list dt {
  color: var(--text-muted);
}

.derived-list dd {
  margin: 0;
  font-variant-numeric: tabular-nums;
  font-weight: 600;
}

.controls-panel {
  background: var(--panel-bg);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 16px 18px 20px;
  position: sticky;
  top: 20px;
  max-height: calc(100vh - 40px);
  overflow-y: auto;
}

.controls-header {
  display: flex;
  gap: 8px;
  margin-bottom: 14px;
  flex-wrap: wrap;
}

.controls-header button {
  flex: 1 1 auto;
  padding: 9px 12px;
  border-radius: 8px;
  border: 1px solid var(--panel-border);
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 600;
  font-size: 0.88rem;
  cursor: pointer;
}

.controls-header button:hover {
  filter: brightness(0.97);
}

.control-group {
  border: none;
  border-top: 1px solid var(--panel-border);
  padding: 10px 0 4px;
  margin: 0;
}

.control-group legend {
  padding: 0 2px 6px 0;
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
}

.control-row {
  display: grid;
  grid-template-columns: 1fr auto auto;
  grid-template-areas: "label label label" "input output unit";
  align-items: center;
  column-gap: 6px;
  padding: 5px 0;
}

.control-row label {
  grid-area: label;
  font-size: 0.86rem;
  color: var(--text);
}

.control-row input[type="range"] {
  grid-area: input;
  width: 100%;
  accent-color: var(--accent);
}

.control-row output {
  grid-area: output;
  font-variant-numeric: tabular-nums;
  font-size: 0.84rem;
  font-weight: 600;
  min-width: 3.2em;
  text-align: right;
}

.control-row .unit {
  grid-area: unit;
  min-width: 4.5em;
  font-size: 0.74rem;
  color: var(--text-muted);
  text-align: left;
}

.control-hint {
  margin: -2px 0 8px;
  font-size: 0.76rem;
  color: var(--text-muted);
  font-style: italic;
}

.order-row {
  grid-template-columns: 1fr;
  grid-template-areas: "label" "input";
}

.segmented {
  grid-area: input;
  display: flex;
  border: 1px solid var(--panel-border);
  border-radius: 8px;
  overflow: hidden;
}

.segmented-option {
  flex: 1 1 0;
  text-align: center;
  padding: 6px 0;
  font-size: 0.86rem;
  font-weight: 600;
  cursor: pointer;
  color: var(--text-muted);
  border-right: 1px solid var(--panel-border);
}

.segmented-option:last-child {
  border-right: none;
}

.segmented-option input {
  position: absolute;
  opacity: 0;
  pointer-events: none;
}

.segmented-option:has(input:checked) {
  background: var(--accent);
  color: #fff;
}

.app-footer {
  max-width: 1200px;
  margin: 0 auto;
  padding: 8px 32px 36px;
  color: var(--text-muted);
  font-size: 0.82rem;
}

.app-footer code {
  background: var(--accent-soft);
  padding: 1px 5px;
  border-radius: 4px;
}

/* --- SVG element styling (shared classes drawn by ray-diagram.js / trace-plot.js) --- */

.grid-line {
  stroke: var(--grid-line);
  stroke-width: 1;
}

.plot-frame {
  fill: none;
  stroke: var(--axis-line);
  stroke-width: 1;
}

.tick-label {
  fill: var(--text-muted);
  font-size: 10px;
}

.axis-title {
  fill: var(--text);
  font-size: 11px;
  font-weight: 600;
}

.trace-segment {
  stroke-width: 2.4;
  stroke-linecap: round;
}

.trace-marker {
  stroke: var(--panel-bg);
  stroke-width: 0.6;
}

.trace-current {
  stroke: var(--text);
  stroke-width: 1.5;
}

.colorbar-frame {
  fill: none;
  stroke: var(--axis-line);
  stroke-width: 1;
}

.scale-bar {
  stroke: var(--text);
  stroke-width: 1.5;
}

.scale-bar-label {
  fill: var(--text);
  font-size: 10px;
  font-weight: 600;
}

.optical-axis {
  stroke: var(--axis-line);
  stroke-width: 1.5;
}

.stage-label {
  fill: var(--text);
  font-size: 11px;
  font-weight: 600;
}

.diagram-title {
  fill: var(--text-muted);
  font-size: 11px;
  text-anchor: middle;
}

.diagram-caption {
  fill: var(--text-muted);
  font-size: 9.5px;
  text-anchor: middle;
}

.icon-lens {
  stroke: var(--axis-line);
  stroke-width: 2;
}

.icon-lens-arc {
  fill: none;
  stroke: var(--accent);
  stroke-width: 2;
}

.icon-grism-body {
  fill: var(--accent-soft);
  stroke: var(--accent);
  stroke-width: 1.5;
}

.icon-grating-line {
  stroke: var(--accent);
  stroke-width: 1;
  opacity: 0.65;
}

.icon-prism {
  fill: var(--accent);
  opacity: 0.18;
  stroke: var(--accent);
  stroke-width: 1;
}

.icon-source {
  stroke: var(--text);
  stroke-width: 1;
}

.icon-detector {
  fill: var(--panel-bg);
  stroke: var(--axis-line);
  stroke-width: 1.5;
}

.lane-title {
  fill: var(--text);
  font-size: 10.5px;
  font-weight: 600;
}

.lane-scale {
  fill: var(--text-muted);
  font-size: 9.5px;
}

.lane-baseline {
  stroke: var(--grid-line);
  stroke-width: 1;
  stroke-dasharray: 3 3;
}

.bend-path {
  fill: none;
  stroke-width: 2;
  opacity: 0.85;
}

.bend-marker {
  stroke: var(--panel-bg);
  stroke-width: 0.6;
}

.bend-label {
  fill: var(--text-muted);
  font-size: 9px;
  text-anchor: middle;
}