/* ── Reset & Tokens ─── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #0d1117; --surface: #161b27; --surface2: #1f2535; --border: #2a3050;
  --accent: #ff4081; --accent-lo: rgba(255,64,129,.22);
  --green: #3ddc84; --red: #ff5555; --gold: #f5c842;
  --text: #dde3f0; --text-dim: #6b7a99;
  --font: 'Segoe UI', system-ui, sans-serif; --mono: 'Courier New', monospace;
  --radius: 12px;
}

body { background: var(--bg); color: var(--text); font-family: var(--font); min-height: 100vh; padding: 0 16px; }
#app { max-width: 1020px; margin: 0 auto; display: flex; flex-direction: column; gap: 14px; }

/* ── Header ─── */
header { text-align: center; padding: 4px 0; }
header h1 {
  font-size: 1.8rem; font-weight: 700;
  background: linear-gradient(120deg, var(--accent) 0%, #ffc2d6 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.subtitle { color: var(--text-dim); font-size: 0.85rem; margin-top: 3px; }

/* ── Controls bar ─── */
.controls-bar {
  display: flex; flex-wrap: wrap; align-items: center; gap: 14px;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.ctrl-group { display: flex; align-items: center; gap: 8px; }
.ctrl-label { font-size: 0.72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-dim); white-space: nowrap; }
.setup-bar { gap: 12px; }
.setup-bar .ctrl-group { min-width: 0; gap: 7px; }

/* ── Medium selects ─── */
.rg-select {
  background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  color: var(--text); padding: 8px 10px; font-size: 0.82rem; font-family: var(--font);
  min-height: 36px; cursor: pointer; max-width: 200px;
  min-width: 0; text-overflow: ellipsis;
}
.rg-select:focus { outline: 2px solid var(--accent); border-color: transparent; }
.rg-select:disabled { opacity: .4; cursor: not-allowed; }

/* a swatch of the medium colour sits beside each selector */
.medium-swatch {
  width: 16px; height: 16px; border-radius: 4px; flex-shrink: 0;
  border: 1px solid rgba(255,255,255,.28); box-shadow: inset 0 0 6px rgba(255,255,255,.18);
}
.n-tag {
  font-family: var(--mono); font-size: 0.78rem; font-weight: 700; color: var(--accent);
  white-space: nowrap; min-width: 58px;
}

/* ── Sliders ─── */
.setup-sliders { flex-direction: column; align-items: stretch; gap: 10px; }
.sim-row { display: flex; align-items: center; gap: 16px; flex-wrap: wrap; }
.sim-slider-group { display: flex; align-items: center; gap: 10px; flex: 1; min-width: 300px; }
.sim-slider-spacer { visibility: hidden; }
.sim-slider-label {
  flex-shrink: 0; min-width: 118px; font-size: 0.76rem; font-weight: 700;
  color: var(--text-dim); white-space: nowrap;
}
.sim-slider {
  flex: 1; min-width: 70px; -webkit-appearance: none; appearance: none; height: 6px;
  background: rgba(255,255,255,.12); border-radius: 3px; outline: none;
  border: 1px solid rgba(255,255,255,.1); cursor: pointer;
}
.sim-slider::-webkit-slider-runnable-track {
  height: 6px; border-radius: 3px;
  background: linear-gradient(to right, var(--accent-lo), rgba(255,255,255,.12));
}
.sim-slider::-webkit-slider-thumb {
  -webkit-appearance: none; width: 18px; height: 18px; margin-top: -6px;
  border-radius: 50%; background: var(--accent); cursor: pointer;
  box-shadow: 0 0 8px var(--accent-lo); border: 2px solid rgba(255,255,255,.2);
}
.sim-slider::-moz-range-track {
  height: 6px; border-radius: 3px; border: none;
  background: linear-gradient(to right, var(--accent-lo), rgba(255,255,255,.12));
}
.sim-slider::-moz-range-thumb {
  width: 16px; height: 16px; border: 2px solid rgba(255,255,255,.2);
  border-radius: 50%; background: var(--accent); cursor: pointer;
}
.sim-slider:disabled { opacity: .4; cursor: not-allowed; }
.sim-slider-val {
  font-family: var(--mono); font-size: 0.85rem; font-weight: 700;
  color: var(--accent); min-width: 74px; text-align: right; flex-shrink: 0;
}

/* the wavelength slider paints the visible spectrum so the value is legible */
#wl-slider::-webkit-slider-runnable-track {
  background: linear-gradient(to right,#7a00ff 0%,#0040ff 14%,#00b3ff 28%,#00ff66 44%,#c8ff00 60%,#ff9100 78%,#ff0000 100%);
}
#wl-slider::-moz-range-track {
  background: linear-gradient(to right,#7a00ff 0%,#0040ff 14%,#00b3ff 28%,#00ff66 44%,#c8ff00 60%,#ff9100 78%,#ff0000 100%);
}

/* ── Stepper ─── */
.stepper-wrap {
  display: flex; align-items: center; gap: 0; flex-shrink: 0;
  border: 1px solid var(--border); border-radius: 8px; overflow: hidden;
  background: var(--bg); height: 36px;
}
.stepper-btn {
  width: 36px; height: 36px; border: none; cursor: pointer;
  font-size: 1rem; font-weight: 700; color: var(--text-dim);
  background: var(--surface2); display: flex; align-items: center; justify-content: center;
  transition: background .15s, color .15s; flex-shrink: 0;
}
.stepper-btn:hover { background: var(--accent-lo); color: var(--accent); }
.stepper-btn:active { background: var(--accent); color: #061318; }
.stepper-btn:focus-visible { outline: 2px solid var(--accent); outline-offset: -2px; }
.stepper-input {
  width: 62px; border: none; text-align: center; height: 100%;
  font-family: var(--mono); font-size: 0.82rem; font-weight: 700;
  color: var(--accent); background: var(--bg); outline: none;
  padding: 4px 2px; -moz-appearance: textfield;
}
.stepper-input:focus { background: var(--surface2); }
.stepper-input:disabled { opacity: .45; cursor: not-allowed; }
.stepper-input::-webkit-outer-spin-button,
.stepper-input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }
.stepper-wrap.locked { opacity: .45; }
.stepper-wrap.locked .stepper-btn { cursor: not-allowed; }

/* ── Pill tabs ─── */
.pill-tabs { display: flex; background: var(--bg); border-radius: 8px; padding: 3px; gap: 2px; flex-wrap: wrap; }
.pill {
  padding: 5px 13px; border: none; background: transparent; color: var(--text-dim);
  border-radius: 6px; cursor: pointer; font-size: 0.81rem;
  transition: background .18s, color .18s, box-shadow .18s;
}
.pill.active { background: var(--accent); color: #2b0512; font-weight: 700; box-shadow: 0 0 12px var(--accent-lo); }
.pill:hover:not(.active) { background: var(--surface2); color: var(--text); }
.pill:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.toggle-chip:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ── Buttons ─── */
.btn {
  padding: 8px 18px; border: none; border-radius: 8px; cursor: pointer;
  font-size: 0.84rem; font-weight: 600; transition: filter .18s, box-shadow .18s, opacity .18s;
}
.btn:disabled { opacity: 0.35; cursor: not-allowed; }
.btn-primary { background: var(--accent); color: #2b0512; font-weight: 700; }
.btn-primary:not(:disabled):hover { filter: brightness(1.12); box-shadow: 0 0 14px var(--accent-lo); }
.btn-ghost { background: var(--surface2); color: var(--text-dim); border: 1px solid var(--border); }
.btn-ghost:hover { background: var(--border); color: var(--text); }

/* ── Toggle chips ─── */
.toggle-chip {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 6px 13px 6px 11px; border-radius: 16px; border: 1px solid var(--border);
  background: var(--bg); color: var(--text-dim); font-size: 0.78rem; cursor: pointer;
  min-height: 36px; transition: all .15s; -webkit-tap-highlight-color: transparent;
}
.toggle-chip::before {
  content: ''; width: 7px; height: 7px; border-radius: 50%; flex-shrink: 0;
  background: transparent; border: 1.5px solid var(--text-dim); transition: all .15s;
}
.toggle-chip:hover { border-color: var(--accent); color: var(--text); }
.toggle-chip:hover::before { border-color: var(--accent); }
.toggle-chip.active { background: var(--accent-lo); border-color: var(--accent); color: var(--accent); font-weight: 600; }
.toggle-chip.active::before { background: var(--accent); border-color: var(--accent); box-shadow: 0 0 6px var(--accent-lo); }

/* ── Canvas card ─── */
.canvas-card {
  width: 100%; background: #080b11;
  border: 1px solid var(--border); border-radius: var(--radius);
  padding: 0; position: relative; overflow-x: clip;
}
/* the cursor is set from JS: crosshair over the bench, grab over the laser,
   grabbing while it is being swung */
.canvas-card canvas { display: block; width: 100%; height: auto; touch-action: pan-y; cursor: crosshair; }

/* ── Collapsible display panel (top-right of canvas) ─── */
.canvas-display {
  position: absolute; top: 10px; right: 10px; z-index: 21;
  width: max-content; max-width: calc(100% - 20px);
  background: rgba(15,20,32,0.80);
  -webkit-backdrop-filter: blur(16px) saturate(160%); backdrop-filter: blur(16px) saturate(160%);
  border: 1px solid rgba(255,255,255,0.10); border-radius: 13px;
  box-shadow: 0 8px 26px rgba(0,0,0,0.45), inset 0 1px 0 rgba(255,255,255,0.06);
  overflow: hidden;
}
.cd-handle {
  display: flex; align-items: center; gap: 8px; width: 100%;
  padding: 8px 11px; background: none; border: none; cursor: pointer;
  color: var(--text); font-size: 0.78rem; font-weight: 700;
  -webkit-tap-highlight-color: transparent;
}
.cd-eye { font-size: 0.9rem; line-height: 1; }
.cd-label { flex: 1; text-align: left; }
.cd-caret { font-size: 0.7rem; color: var(--text-dim); transition: transform .2s; }
.canvas-display[data-collapsed="true"] .cd-caret { transform: rotate(180deg); }
.canvas-display[data-collapsed="true"] .cd-body { display: none; }
.cd-body { padding: 2px 10px 10px; max-height: 62vh; overflow-y: auto; }
.display-toggles { display: flex; flex-direction: column; gap: 5px; align-items: stretch; min-width: 148px; }
.cd-group-label {
  font-size: 0.66rem; text-transform: uppercase; letter-spacing: .07em;
  color: var(--text-dim); font-weight: 700; margin: 7px 0 1px 2px;
}
.canvas-display .toggle-chip {
  min-height: 30px; padding: 5px 11px 5px 9px; gap: 7px;
  font-size: 0.74rem; background: rgba(13,17,23,0.5); justify-content: flex-start;
}
.canvas-display .toggle-chip::before { width: 6px; height: 6px; }
#btn-sound::before { display: none; }
#btn-sound .snd-ico { font-size: 0.9rem; line-height: 1; margin-right: -1px; }

/* ── Canvas action dock (bottom of canvas) ─── */
.canvas-dock {
  position: absolute; left: 10px; right: 10px; bottom: 10px; z-index: 20;
  display: flex; align-items: center; gap: 8px; flex-wrap: wrap;
  padding: 7px 9px; border-radius: 12px;
  background: rgba(15,20,32,0.78);
  -webkit-backdrop-filter: blur(16px) saturate(160%); backdrop-filter: blur(16px) saturate(160%);
  border: 1px solid rgba(255,255,255,0.10);
  box-shadow: 0 8px 26px rgba(0,0,0,0.45), inset 0 1px 0 rgba(255,255,255,0.06);
}
.dock-actions { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.dock-btn {
  display: inline-flex; align-items: center; gap: 6px; min-height: 36px;
  padding: 6px 14px; border-radius: 9px; border: 1px solid rgba(255,255,255,0.12);
  background: rgba(13,17,23,0.55); color: var(--text); font-size: 0.79rem; font-weight: 600;
  cursor: pointer; white-space: nowrap; flex-shrink: 0;
  transition: filter .15s, border-color .15s, color .15s, background .15s;
  -webkit-tap-highlight-color: transparent;
  -webkit-user-select: none; user-select: none; -webkit-touch-callout: none; touch-action: manipulation;
}
.dock-btn:hover { border-color: var(--accent); color: #fff; background: var(--accent-lo); }
.dock-btn:disabled { opacity: .35; cursor: not-allowed; }
.dock-btn.holding { background: var(--accent); border-color: var(--accent); color: #2b0512; box-shadow: 0 0 14px var(--accent-lo); }
.dock-btn-accent { background: var(--accent-lo); border-color: var(--accent); color: var(--accent); }
.dock-btn-accent:hover { background: var(--accent); color: #2b0512; }
.dock-btn-play.running { background: rgba(61,220,132,.16); border-color: var(--green); color: var(--green); }
/* A non-ideal condition switched on deliberately (friction). Gold, not red:
   it is not an error, it is the interesting case. */
.dock-btn-warn { background: rgba(245,200,66,.16); border-color: var(--gold); color: var(--gold); }
.dock-btn-warn:hover { background: rgba(245,200,66,.28); color: #fff5d6; border-color: var(--gold); }

/* The lamp switch. Unlit it is the one call to action on the bench, so it
   glows gently; lit it goes green like every other running state on the site. */
.dock-btn-fire {
  background: var(--accent-lo); border-color: var(--accent); color: var(--accent); font-weight: 700;
  animation: fire-pulse 2.4s ease-in-out infinite;
}
.dock-btn-fire:hover { background: var(--accent); color: #2b0512; }
.dock-btn-fire.lit {
  background: rgba(61,220,132,.16); border-color: var(--green); color: var(--green);
  animation: none;
}
.dock-btn-fire.lit:hover { background: rgba(61,220,132,.28); color: #eafff3; }
@keyframes fire-pulse {
  0%, 100% { box-shadow: 0 0 0 rgba(255,64,129,0); }
  50%      { box-shadow: 0 0 14px var(--accent-lo); }
}
@media (prefers-reduced-motion: reduce) { .dock-btn-fire { animation: none; } }

/* ── Readout panel ─── */
.readout-panel {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(158px, 1fr)); gap: 10px;
  padding: 14px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.readout-cell {
  background: var(--surface2); border-radius: 8px; padding: 10px 14px;
  display: flex; flex-direction: column; gap: 2px;
}
.ro-label { font-size: 0.72rem; color: var(--text-dim); text-transform: uppercase; letter-spacing: .04em; }
.ro-value { font-size: 1.1rem; font-weight: 700; color: var(--text); font-family: var(--mono); }
.ro-hero { font-size: 1.4rem; color: var(--accent); }
.ro-value.ok { color: var(--green); }
.ro-value.warn { color: var(--gold); }
.ro-value.bad { color: var(--red); }

/* ── Learn / results cards ─── */
.learn-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); overflow: hidden; transition: border-color .18s;
}
.learn-card[open] { border-color: var(--accent); }
.learn-card > summary {
  list-style: none; cursor: pointer; padding: 10px 14px; display: flex; align-items: center;
  gap: 10px; flex-wrap: wrap; font-size: 0.88rem; font-weight: 700; color: var(--text);
  user-select: none; transition: background .15s;
}
.learn-card > summary::-webkit-details-marker { display: none; }
.learn-card > summary::after { content: '\25BE'; margin-left: auto; color: var(--text-dim); font-size: 0.78rem; transition: transform .2s; }
.learn-card[open] > summary::after { transform: rotate(180deg); color: var(--accent); }
.lp-badge {
  display: inline-flex; align-items: center; justify-content: center; width: 22px; height: 22px;
  border-radius: 6px; background: var(--accent-lo); font-size: 0.9rem; flex-shrink: 0; color: var(--accent);
}
.lp-sub { color: var(--text-dim); font-weight: 500; font-size: 0.78rem; }
.learn-body { padding: 12px 14px 14px; font-size: 0.84rem; color: var(--text-dim); line-height: 1.7; }
.learn-body .eq-line {
  font-size: 0.95rem; color: var(--text); background: var(--surface2);
  border-left: 3px solid var(--accent); padding: 8px 10px; border-radius: 6px;
  margin: 6px 0; overflow-x: auto;
}
.learn-body .eq-note { font-size: 0.8rem; color: var(--text-dim); margin: 4px 0 10px; }

/* ── Calculation modal ─── */
.calc-modal {
  position: fixed; inset: 0; z-index: 1000; display: flex;
  align-items: center; justify-content: center; padding: 20px;
  background: rgba(5,8,14,0.72); -webkit-backdrop-filter: blur(4px); backdrop-filter: blur(4px);
}
.calc-box {
  width: 100%; max-width: 620px; max-height: 84vh; display: flex; flex-direction: column;
  background: var(--surface); border: 1px solid var(--accent); border-radius: var(--radius);
  box-shadow: 0 20px 60px rgba(0,0,0,0.6);
}
.calc-head {
  display: flex; align-items: center; gap: 10px; padding: 14px 18px;
  border-bottom: 1px solid var(--border); font-size: 0.95rem; font-weight: 700; color: var(--accent);
}
.calc-close {
  margin-left: auto; background: none; border: none; color: var(--text-dim);
  font-size: 1.5rem; line-height: 1; cursor: pointer; padding: 0 4px; transition: color .15s;
}
.calc-close:hover { color: var(--red); }
.calc-body { padding: 16px 18px; overflow-y: auto; font-size: 0.85rem; color: var(--text-dim); line-height: 1.75; }
.calc-body .eq-line {
  font-size: 0.95rem; color: var(--text); background: var(--surface2);
  border-left: 3px solid var(--accent); padding: 8px 10px; border-radius: 6px;
  margin: 6px 0; overflow-x: auto;
}
.calc-body h4 { color: var(--text); font-size: 0.88rem; margin: 14px 0 4px; }
.calc-body h4:first-child { margin-top: 0; }

/* ── Explore mode ─── */
.explore-cards { display: grid; grid-template-columns: 1fr; gap: 12px; }
.explore-card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 18px 20px; transition: border-color .18s;
}
.explore-card:hover { border-color: var(--accent); }
.explore-card h3 { font-size: 1rem; color: var(--accent); margin-bottom: 6px; }
.explore-card .ec-formula {
  font-family: var(--mono); font-size: 0.88rem; color: var(--gold);
  background: var(--bg); padding: 6px 12px; border-radius: 6px; margin: 8px 0;
  display: inline-block;
}
.explore-card p { font-size: 0.88rem; color: var(--text-dim); line-height: 1.55; }
.explore-card .ec-example {
  margin-top: 8px; padding: 10px 14px; background: var(--surface2);
  border-radius: 8px; font-size: 0.84rem; color: var(--text); line-height: 1.5;
}

/* ── Practice & Quiz ─── */
.practice-bar {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.pbar-score { font-size: 0.84rem; color: var(--text-dim); margin-left: auto; }
.pbar-score span { color: var(--text); font-weight: 700; }
.practice-question {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px 22px;
}
.pq-text { font-size: 0.95rem; line-height: 1.6; margin-bottom: 12px; }
.pq-input-row { display: flex; align-items: center; gap: 8px; margin-bottom: 10px; }
.pq-input-row input {
  background: var(--bg); border: 1px solid var(--border); border-radius: 6px;
  color: var(--text); padding: 8px 12px; font-size: 1rem; font-family: var(--mono); width: 180px;
}
.pq-input-row input:focus { outline: 2px solid var(--accent); border-color: transparent; }
.pq-unit { font-size: 0.88rem; color: var(--text-dim); }
.feedback { font-size: 0.88rem; font-weight: 600; }
.feedback.ok { color: var(--green); }
.feedback.err { color: var(--red); }
.solution {
  margin-top: 10px; padding: 12px 16px; background: var(--surface2);
  border-radius: 8px; font-size: 0.84rem; line-height: 1.7; color: var(--text-dim);
  white-space: pre-line;
}

/* ── MCQ options ─── */
.pq-mcq, .qq-options { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin-bottom: 12px; }
.pq-opt, .qq-opt {
  padding: 10px 14px; background: var(--surface2); border: 1px solid var(--border);
  border-radius: 8px; cursor: pointer; font-size: 0.88rem; color: var(--text);
  transition: all .18s; text-align: left;
}
.pq-opt:hover, .qq-opt:hover { border-color: var(--accent); background: var(--accent-lo); }
.pq-opt.selected, .qq-opt.selected { border-color: var(--accent); background: var(--accent-lo); }
.pq-opt.correct, .qq-opt.correct { border-color: var(--green); background: rgba(61,220,132,.15); }
.pq-opt.wrong, .qq-opt.wrong { border-color: var(--red); background: rgba(255,85,85,.15); }

/* ── Quiz result ─── */
.quiz-result {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px 22px;
}
.qr-header { text-align: center; margin-bottom: 16px; }
.qr-score { font-size: 2rem; font-weight: 700; }
.qr-score.perfect { color: var(--gold); }
.qr-score.good { color: var(--green); }
.qr-score.poor { color: var(--red); }
.qr-stars { font-size: 1.5rem; margin-top: 4px; }
.qr-rows { display: flex; flex-direction: column; gap: 8px; margin-top: 12px; }
.qr-row { padding: 10px 14px; background: var(--surface2); border-radius: 8px; font-size: 0.84rem; line-height: 1.5; }
.qr-row.ok { border-left: 3px solid var(--green); }
.qr-row.err { border-left: 3px solid var(--red); }

/* ── Context menu ─── */
.ctx-menu {
  position: fixed; z-index: 999;
  background: var(--surface2); border: 1px solid var(--border);
  border-radius: 8px; padding: 4px 0; min-width: 178px;
  box-shadow: 0 8px 24px rgba(0,0,0,0.55);
}
.ctx-menu button {
  display: block; width: 100%; padding: 9px 16px; text-align: left;
  background: none; border: none; color: var(--text); font-size: 0.85rem;
  cursor: pointer; transition: background .15s;
}
.ctx-menu button:hover { background: var(--accent-lo); color: var(--accent); }
.ctx-menu hr { border: none; border-top: 1px solid var(--border); margin: 3px 0; }

/* ── SEO article ─── */
.seo-article {
  padding: 28px 22px; margin-top: 10px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.seo-article h2 { font-size: 1.25rem; color: var(--accent); margin-bottom: 12px; }
.seo-article h3 { font-size: 1.05rem; color: var(--text); margin: 18px 0 8px; }
.seo-article p { font-size: 0.9rem; color: var(--text-dim); line-height: 1.65; margin-bottom: 10px; }
.seo-article a { color: var(--accent); text-decoration: none; }
.seo-article a:hover { text-decoration: underline; }

/* ── Featured snippet table ─── */
.snippet-table {
  width: 100%; border-collapse: collapse; font-size: 0.85rem;
  margin: 12px 0; border-radius: 8px; overflow: hidden;
}
.snippet-table th {
  background: var(--surface2); color: var(--text-dim);
  padding: 9px 12px; text-align: left; font-size: 0.78rem;
  text-transform: uppercase; letter-spacing: .04em; font-weight: 600;
}
.snippet-table td { padding: 8px 12px; border-top: 1px solid var(--border); color: var(--text-dim); }
.snippet-table tr:hover td { background: var(--surface2); color: var(--text); }
.snippet-table td:nth-child(2) { font-family: var(--mono); font-weight: 700; color: var(--text); }

/* ── Readings table (sin i / sin r) ─── */
.data-table { width: 100%; border-collapse: collapse; font-size: 0.85rem; }
.data-table th {
  background: var(--surface2); color: var(--text-dim); padding: 8px 10px; text-align: left;
  font-size: 0.72rem; text-transform: uppercase; letter-spacing: .04em; font-weight: 700; white-space: nowrap;
}
.data-table td { padding: 7px 10px; border-top: 1px solid var(--border); color: var(--text); font-family: var(--mono); white-space: nowrap; }
.data-table tr.tir td { color: var(--gold); }
.data-table td .row-del {
  background: none; border: none; color: var(--text-dim); cursor: pointer;
  font-size: 1rem; line-height: 1; padding: 0 4px;
}
.data-table td .row-del:hover { color: var(--red); }
.data-empty { color: var(--text-dim); font-size: 0.84rem; padding: 14px 4px; }
.data-summary { margin-top: 12px; font-size: 0.85rem; line-height: 1.7; color: var(--text-dim); }
.data-summary strong { color: var(--text); }
.data-summary .mean { font-family: var(--mono); font-size: 1.1rem; color: var(--accent); font-weight: 700; }
.data-actions { margin-top: 12px; display: flex; gap: 8px; flex-wrap: wrap; }

/* ── Unknown-medium determination ─── */
.unknown-box {
  margin-top: 14px; padding: 14px 16px; background: var(--surface2);
  border: 1px dashed var(--accent); border-radius: 8px;
}
.unknown-box label { display: block; font-size: 0.78rem; font-weight: 700; color: var(--accent); margin-bottom: 8px; }
.unk-row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.unk-row input {
  width: 130px; height: 40px; padding: 0 10px; border: 1px solid var(--border); border-radius: 8px;
  background: var(--bg); color: var(--accent); font-family: var(--mono); font-size: 0.95rem;
  font-weight: 700; outline: none; -moz-appearance: textfield;
}
.unk-row input::-webkit-outer-spin-button,
.unk-row input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }
.unk-feedback { margin-top: 10px; font-size: 0.85rem; line-height: 1.6; }
.unk-feedback.ok { color: var(--green); }
.unk-feedback.close { color: var(--gold); }
.unk-feedback.err { color: var(--red); }
#btn-unknown { padding: 6px 12px 6px 10px; font-size: 0.76rem; white-space: nowrap; }

/* An action chip fires a preset rather than holding a state, so it drops the
   status dot the toggle chips carry and takes the accent outline instead. */
.chip-action { padding: 6px 13px; font-size: 0.76rem; white-space: nowrap; border-color: var(--gold); color: var(--gold); }
.chip-action::before { display: none; }
.chip-action:hover:not(:disabled) { background: rgba(245,200,66,.16); border-color: var(--gold); color: var(--gold); }
.chip-action:disabled { opacity: .38; cursor: not-allowed; }
#btn-unknown.active { background: var(--accent-lo); border-color: var(--accent); color: var(--accent); font-weight: 700; }
.unknown-hint {
  flex: 1 1 100%; margin: 4px 0 0; padding: 9px 13px;
  background: var(--accent-lo); border-left: 3px solid var(--accent);
  border-radius: 6px; font-size: 0.8rem; line-height: 1.6; color: var(--text);
}
.unknown-hint strong { color: var(--accent); }
.sim-slider-group.locked .sim-slider-label,
.setup-bar .ctrl-group.locked .ctrl-label { opacity: .55; }

/* ── Calculate mode ─── */
.calc-panel {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 18px 20px;
  display: flex; flex-direction: column; gap: 14px;
}
.calc-intro { font-size: 0.88rem; color: var(--text-dim); line-height: 1.6; margin: 0; }
.calc-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 12px; }
.calc-field { display: flex; flex-direction: column; gap: 5px; }
.calc-field label { font-size: 0.74rem; font-weight: 700; color: var(--text-dim); }
.calc-field .cf-wrap { display: flex; align-items: center; gap: 0; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; background: var(--bg); height: 42px; }
.calc-field input {
  flex: 1; min-width: 0; border: none; background: transparent; height: 100%;
  color: var(--accent); font-family: var(--mono); font-size: 0.95rem; font-weight: 700;
  padding: 0 10px; outline: none; -moz-appearance: textfield;
}
.calc-field input::-webkit-outer-spin-button,
.calc-field input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }
.calc-field input:focus { background: var(--surface2); }
.calc-field .cf-unit { font-size: 0.78rem; color: var(--text-dim); font-weight: 600; padding: 0 11px; white-space: nowrap; }
.calc-field.unknown .cf-wrap { border-color: var(--accent); border-style: dashed; }
.calc-field.unknown label { color: var(--accent); }
.calc-result {
  background: var(--surface2); border-left: 3px solid var(--accent);
  border-radius: 8px; padding: 14px 16px;
}
.cr-label { font-size: 0.74rem; text-transform: uppercase; letter-spacing: .05em; color: var(--text-dim); }
.cr-value { font-family: var(--mono); font-size: 1.6rem; font-weight: 700; color: var(--accent); margin-top: 3px; }
.cr-sub { font-size: 0.8rem; color: var(--text-dim); margin-top: 5px; line-height: 1.5; }
.cr-value.bad { color: var(--red); font-size: 1rem; }

/* ── Utility ─── */
.hidden { display: none !important; }

/* ── Responsive ─── */
@media (max-width: 768px) {
  .readout-panel { grid-template-columns: 1fr 1fr; }
  .controls-bar { gap: 10px; }
  .qq-options, .pq-mcq { grid-template-columns: 1fr; }
  .setup-bar .ctrl-group { flex: 1 1 100%; min-width: 0; }
  .rg-select { max-width: 100%; width: 100%; flex: 1 1 auto; min-width: 0; }
  .sim-slider-group { flex: 1 1 100%; min-width: 0; flex-wrap: wrap; }
  .sim-slider-spacer { display: none; }
  .sim-slider-label { min-width: 96px; font-size: 0.74rem; }
  @media (max-width: 560px) {
    .sim-slider-group { row-gap: 8px; }
    .sim-slider { flex: 1 1 100%; order: 2; min-width: 0; }
    .sim-slider-label { order: 0; flex: 1 1 auto; }
    .sim-slider-val { order: 1; }
    .stepper-wrap { order: 3; height: 44px; margin-left: auto; }
    .stepper-btn { width: 44px; height: 44px; }
    .stepper-input { width: 76px; font-size: 0.88rem; }
  }
}

@media (max-width: 500px) {
  header h1 { font-size: 1.4rem; }
  .subtitle { font-size: 0.78rem; }
  .controls-bar { padding: 10px 12px; gap: 8px; }
  .pill { padding: 5px 10px; font-size: 0.76rem; }
  .readout-panel { grid-template-columns: 1fr; }
  .practice-question { padding: 14px 16px; }
  .calc-panel { padding: 14px 15px; }
  .cr-value { font-size: 1.3rem; }
  .ro-value { font-size: 1rem; }
  .ro-hero { font-size: 1.2rem; }
}

/* INTERLINK-START  header quick-links */
.head-actions{display:flex;align-items:center;gap:8px;margin-left:auto;flex-wrap:wrap;justify-content:flex-end;}
.btn-link{display:inline-flex;align-items:center;gap:7px;padding:5px 12px;border-radius:8px;font-size:.82rem;font-weight:700;text-decoration:none;cursor:pointer;background:var(--surface2,#1f2535);color:var(--text,#dde3f0);border:1.5px solid var(--border,#2a3050);white-space:nowrap;transition:border-color .18s,background .18s,color .18s;}
.btn-link:hover{border-color:var(--accent,#22d3ee);background:var(--accent-lo,rgba(34,211,238,.18));color:#fff;}
.btn-link img{width:20px;height:20px;border-radius:4px;flex:none;}
.btn-link .lbl{line-height:1;}
@media(max-width:560px){.btn-link .lbl{display:none;}.btn-link{padding:5px 9px;}}
/* INTERLINK-END */


/* ══════════════════════════════════════════════════════════════════
   Collision & Momentum — tool-specific blocks
   ══════════════════════════════════════════════════════════════════ */

/* ── Apparatus picker: pills that carry a tiny glyph ─── */
.appa-tabs { display: flex; flex-wrap: wrap; gap: 6px; }
.appa-tabs .pill { display: inline-flex; align-items: center; gap: 6px; }
.appa-ico { font-size: 0.95rem; line-height: 1; }

/* ── Body (glider / puck / cart) identity chips ───
   Body 1 is always the accent hue, body 2 the gold hue, so the colour in the
   readout always matches the colour on the canvas. */
.body-swatch {
  width: 14px; height: 14px; border-radius: 4px; flex-shrink: 0;
  border: 1px solid rgba(255,255,255,.3); box-shadow: inset 0 0 6px rgba(255,255,255,.2);
}
.body-swatch.b1 { background: #ff4081; }
.body-swatch.b2 { background: #f5c842; }
.body-swatch.b3 { background: #4f8ef7; }
.sim-slider-label .body-swatch { display: inline-block; vertical-align: -2px; margin-right: 5px; }
/* Filled track: the portion left of the thumb is solid accent, so the value
   is readable at a glance without looking at the number. --pct is written by
   the slider builder in app.js on every change. */
.sim-slider::-webkit-slider-runnable-track {
  background: linear-gradient(to right,
    var(--sl-col, var(--accent)) 0%, var(--sl-col, var(--accent)) var(--pct, 0%),
    rgba(255,255,255,.12) var(--pct, 0%), rgba(255,255,255,.12) 100%);
}
.sim-slider::-moz-range-track {
  background: linear-gradient(to right,
    var(--sl-col, var(--accent)) 0%, var(--sl-col, var(--accent)) var(--pct, 0%),
    rgba(255,255,255,.12) var(--pct, 0%), rgba(255,255,255,.12) 100%);
}
.sim-slider::-webkit-slider-thumb { background: var(--sl-col, var(--accent)); }
.sim-slider::-moz-range-thumb     { background: var(--sl-col, var(--accent)); }
/* body 2's controls are gold, matching its colour on the canvas */
#sl-tr-m2, #sl-tr-u2, #sl-tb-m2, #sl-tb-u2, #sl-pd-M, #sl-cs-m2, #sl-cs-v2 { --sl-col: #f5c842; }

/* ── Secondary graph canvas (momentum bars / force-time curve) ─── */
.graph-card {
  width: 100%; background: #080b11; position: relative;
  border: 1px solid var(--border); border-radius: var(--radius); overflow-x: clip;
}
.graph-card canvas { display: block; width: 100%; height: auto; touch-action: pan-y; }
.graph-tabs { position: absolute; top: 6px; right: 8px; z-index: 5; display: flex; gap: 5px; }
.graph-tabs .pill { padding: 4px 10px; font-size: 0.72rem; min-height: 30px; }

/* ── Conservation ledger: the heart of the pedagogy ───
   Before | After | Change, for momentum and kinetic energy, with a verdict
   chip that goes green when the quantity is conserved. */
.ledger { padding: 0; }
.ledger-table { width: 100%; border-collapse: collapse; font-family: var(--mono); font-size: 0.82rem; }
.ledger-table th {
  text-align: right; padding: 7px 10px; font-family: var(--font);
  font-size: 0.68rem; text-transform: uppercase; letter-spacing: .06em;
  color: var(--text-dim); border-bottom: 1px solid var(--border); font-weight: 700;
}
.ledger-table th:first-child { text-align: left; }
.ledger-table td { padding: 7px 10px; text-align: right; border-bottom: 1px solid rgba(42,48,80,.5); color: var(--text); }
.ledger-table td:first-child { text-align: left; font-family: var(--font); color: var(--text-dim); font-size: 0.78rem; }
.ledger-table tr:last-child td { border-bottom: none; }
.ledger-table tr.hero td { font-weight: 700; }
.ledger-table tr.hero td:first-child { color: var(--text); }
.lg-ok   { color: var(--green); }
.lg-loss { color: var(--red); }
.verdict {
  display: inline-flex; align-items: center; gap: 6px; padding: 3px 10px;
  border-radius: 999px; font-family: var(--font); font-size: 0.72rem; font-weight: 700;
  border: 1px solid transparent; white-space: nowrap;
}
.verdict.ok   { background: rgba(61,220,132,.14); border-color: var(--green); color: var(--green); }
.verdict.warn { background: rgba(245,200,66,.14); border-color: var(--gold);  color: var(--gold); }
.verdict.bad  { background: rgba(255,85,85,.14);  border-color: var(--red);   color: var(--red); }

/* ── Readout badges strip (hidden in Practice/Quiz) ─── */
.readout-badges {
  display: flex; flex-wrap: wrap; gap: 8px; padding: 10px 14px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.readout-badge {
  display: inline-flex; align-items: center; gap: 7px; padding: 5px 11px;
  border-radius: 999px; background: var(--surface2); border: 1px solid var(--border);
  font-size: 0.76rem; color: var(--text-dim); white-space: nowrap;
}
.readout-badge strong { font-family: var(--mono); font-size: 0.86rem; color: var(--text); font-weight: 700; }
.rb-dot { width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0; }

/* ── Compact set-up bar ───
   Rig, collision type, preset and units on one strip directly under the
   canvas. Everything here is a size-down of the shared control styles, so
   the whole experiment definition fits in one or two rows instead of four. */
.compact-bar { gap: 10px 16px; padding: 9px 14px; row-gap: 8px; }
.compact-bar .ctrl-group { gap: 6px; }
.compact-bar .ctrl-label { font-size: 0.66rem; letter-spacing: .07em; }
.compact-bar .pill-tabs { gap: 2px; padding: 2px; }
.compact-bar .pill { padding: 5px 10px; font-size: 0.76rem; min-height: 30px; }
.compact-bar .appa-tabs .pill { gap: 5px; }
.compact-bar .appa-ico { font-size: 0.85rem; }

/* the preset dropdown replaces what used to be a three-line chip row */
.preset-select {
  min-height: 32px; padding: 5px 26px 5px 10px; font-size: 0.78rem; max-width: 220px;
  border-style: dashed; color: var(--text-dim);
  background-image: linear-gradient(45deg, transparent 50%, var(--text-dim) 50%),
                    linear-gradient(135deg, var(--text-dim) 50%, transparent 50%);
  background-position: calc(100% - 14px) 55%, calc(100% - 9px) 55%;
  background-size: 5px 5px, 5px 5px;
  background-repeat: no-repeat;
  -webkit-appearance: none; appearance: none;
}
.preset-select:hover { border-color: var(--accent); color: var(--text); border-style: solid; }
.preset-select option { color: var(--text); background: var(--surface); }

/* ── Reference data tables inside Explore cards ─── */
.ref-table { width: 100%; border-collapse: collapse; font-size: 0.8rem; margin-top: 8px; }
.ref-table th {
  background: var(--surface2); color: var(--text-dim); text-align: left; padding: 7px 9px;
  font-size: 0.7rem; text-transform: uppercase; letter-spacing: .05em; font-weight: 700;
  border-bottom: 1px solid var(--border);
}
.ref-table td { padding: 6px 9px; border-bottom: 1px solid rgba(42,48,80,.5); color: var(--text); }
.ref-table td:first-child { color: var(--text-dim); }
.ref-table tr:last-child td { border-bottom: none; }
.ref-table tr:hover td { background: rgba(255,64,129,.06); }
.ref-scroll { overflow-x: auto; max-width: 100%; }
.ref-src { font-size: 0.7rem; color: var(--text-dim); margin-top: 6px; font-style: italic; }

/* ── Explore card sizing for the wider data cards ─── */
.explore-card.wide { grid-column: 1 / -1; }

/* ── Calculate mode: the solved-for field is highlighted ─── */
.calc-hint {
  font-size: 0.76rem; color: var(--text-dim); margin: 2px 0 10px; line-height: 1.55;
}
.calc-hint code { font-family: var(--mono); color: var(--accent); }

/* ── Lab-report / data-log table actions ─── */
.log-table { width: 100%; border-collapse: collapse; font-family: var(--mono); font-size: 0.76rem; }
.log-table th {
  background: var(--surface2); color: var(--text-dim); padding: 6px 8px; text-align: right;
  font-family: var(--font); font-size: 0.68rem; text-transform: uppercase; letter-spacing: .05em;
  border-bottom: 1px solid var(--border); white-space: nowrap;
}
.log-table th:first-child { text-align: left; }
.log-table td { padding: 6px 8px; text-align: right; border-bottom: 1px solid rgba(42,48,80,.5); white-space: nowrap; }
.log-table td:first-child { text-align: left; }
.log-empty { color: var(--text-dim); font-size: 0.8rem; padding: 10px 2px; }

@media (max-width: 768px) {
  .compact-bar .ctrl-group { flex: 1 1 100%; }
  .compact-bar .pill-tabs { flex: 1 1 auto; }
  .compact-bar .pill { min-height: 38px; font-size: 0.78rem; flex: 1 1 auto; }
  .preset-select { max-width: 100%; width: 100%; min-height: 38px; }
  .ledger-table { font-size: 0.76rem; }
  .ledger-table th, .ledger-table td { padding: 6px 6px; }
  .graph-tabs .pill { min-height: 34px; }
}
@media (max-width: 500px) {
  .readout-badge { font-size: 0.72rem; }
  .ledger-table th, .ledger-table td { padding: 5px 4px; }
}

/* The floating display panel and action dock cover part of the drawing. On a
   phone they covered most of it; but the dock also WRAPS to two rows once its
   six buttons no longer fit on one line, which happens around 790px and hides
   a quarter of the bench. So the cut-over to static blocks is at 900px, not
   720px — comfortably wider than any width at which the dock wraps.
   This block must stay LAST — later rules would override the 44px tap sizes. */
@media (max-width: 900px) {
  .canvas-display {
    position: static; width: auto; max-width: none; margin: 0 0 8px;
    background: var(--surface2); border-color: var(--border);
    -webkit-backdrop-filter: none; backdrop-filter: none; box-shadow: none;
  }
  .cd-body { max-height: none; overflow-y: visible; }
  .display-toggles { flex-direction: row; flex-wrap: wrap; min-width: 0; }
  .cd-group-label { flex: 1 1 100%; margin: 6px 0 0 2px; }
  .canvas-display .toggle-chip { min-height: 44px; font-size: 0.78rem; padding: 8px 13px 8px 11px; }
  .canvas-dock {
    position: static; left: auto; right: auto; bottom: auto;
    margin: 8px 0 0; flex-wrap: wrap; justify-content: flex-start;
    background: var(--surface2); border-color: var(--border);
    -webkit-backdrop-filter: none; backdrop-filter: none; box-shadow: none;
  }
  .dock-btn { min-height: 44px; }
}