:root {
  --green: #22c670;
  --green-dark: #119655;
  --night: #061914;
  --ink: #122033;
  --cream: #f4fbf7;
  --paper: #fdfffe;
  --mint: #e3f7ec;
  --mint-strong: #caefdb;
  --line: #d4e9dd;
  --muted: #587065;
  --coral: #dc4c55;
  --gold: #f5c542;
  --shadow: 0 20px 54px rgba(5, 50, 27, .12);
  --shadow-soft: 0 8px 22px rgba(34, 198, 112, .16);
  --radius: 18px;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { min-height: 100%; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  min-width: 320px;
  min-height: 100%;
  color: var(--ink);
  background: var(--cream);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.45;
}
button, input { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
button { color: inherit; }
button:focus-visible, a:focus-visible, input:focus-visible, summary:focus-visible {
  outline: 3px solid var(--green-dark);
  outline-offset: 3px;
}
.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;
}

/* Curiosity-first entry ------------------------------------------------ */
.curiosity-screen {
  position: relative;
  width: 100%;
  height: 100svh;
  min-height: 520px;
  overflow: hidden;
  isolation: isolate;
  background: var(--paper);
}
#curiosity-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
}
.entry-brand, .lab-brand {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  color: var(--night);
  text-decoration: none;
  font-weight: 850;
  letter-spacing: -.02em;
}
.entry-brand {
  position: absolute;
  z-index: 2;
  top: max(18px, env(safe-area-inset-top));
  left: max(20px, env(safe-area-inset-left));
  padding: 7px 11px;
  border: 1px solid rgba(17, 150, 85, .16);
  border-radius: 12px;
  background: rgba(253, 255, 254, .84);
  box-shadow: 0 5px 18px rgba(5, 50, 27, .07);
  backdrop-filter: blur(10px);
}
.entry-brand img, .lab-brand img { display: block; height: 29px; max-width: 150px; object-fit: contain; }
.entry-brand span, .lab-brand span { display: none; }
.icon-button, .icon-only-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--line);
  background: rgba(253, 255, 254, .88);
  cursor: pointer;
  box-shadow: 0 5px 18px rgba(5, 50, 27, .07);
}
.icon-button svg, .icon-only-button svg, .primary-button svg {
  width: 18px;
  height: 18px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.entry-pause {
  position: absolute;
  z-index: 2;
  top: max(18px, env(safe-area-inset-top));
  right: max(20px, env(safe-area-inset-right));
  gap: 7px;
  min-height: 42px;
  padding: 8px 13px;
  border-radius: 12px;
  font-weight: 750;
  backdrop-filter: blur(10px);
}
.entry-invitation {
  position: absolute;
  z-index: 2;
  left: 50%;
  bottom: max(34px, calc(env(safe-area-inset-bottom) + 20px));
  transform: translateX(-50%);
  display: grid;
  justify-items: center;
  gap: 12px;
  width: min(90vw, 380px);
}
.entry-invitation p {
  margin: 0;
  color: var(--night);
  font-size: clamp(1.15rem, 2vw, 1.45rem);
  font-weight: 800;
  letter-spacing: -.02em;
  text-shadow: 0 2px 10px var(--paper);
}

/* Shared controls ------------------------------------------------------ */
.primary-button, .quiet-button, .answer-options button, .canvas-action {
  min-height: 42px;
  border-radius: 11px;
  border: 1px solid var(--line);
  padding: 9px 14px;
  font-weight: 800;
  text-decoration: none;
  cursor: pointer;
  transition: transform .16s ease, box-shadow .16s ease, border-color .16s ease, background-color .16s ease;
}
.primary-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 7px;
  color: var(--night);
  border-color: var(--green);
  background: var(--green);
  box-shadow: var(--shadow-soft);
}
.primary-button:hover { transform: translateY(-1px); box-shadow: 0 12px 26px rgba(34, 198, 112, .24); }
.quiet-button, .answer-options button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--ink);
  background: var(--paper);
}
.quiet-button:hover, .answer-options button:hover { border-color: var(--green); background: var(--cream); }
.small { min-height: 36px; padding: 7px 11px; font-size: .88rem; }

/* Lab shell ------------------------------------------------------------ */
.lab-screen {
  min-height: 100svh;
  padding: max(12px, env(safe-area-inset-top)) clamp(12px, 2vw, 28px) max(18px, env(safe-area-inset-bottom));
  background:
    radial-gradient(900px 440px at 48% -180px, #dff7ea 0%, rgba(223, 247, 234, 0) 72%),
    var(--cream);
}
.lab-header {
  width: min(1760px, 100%);
  min-height: 60px;
  margin: 0 auto 10px;
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: 18px;
}
.lab-brand {
  min-height: 46px;
  padding: 7px 11px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--paper);
  box-shadow: 0 5px 18px rgba(5, 50, 27, .06);
}
.eyebrow, .section-number {
  display: block;
  color: var(--green-dark);
  font-size: .68rem;
  font-weight: 900;
  letter-spacing: .105em;
  text-transform: uppercase;
}
.lab-heading h1 {
  margin: 1px 0 0;
  color: var(--night);
  font-size: clamp(1.1rem, 1.8vw, 1.55rem);
  line-height: 1.15;
  letter-spacing: -.025em;
}
.header-actions { display: flex; align-items: center; gap: 8px; }
.header-actions .quiet-button { font-size: .8rem; min-height: 38px; }

.investigation-tabs {
  width: min(1760px, 100%);
  margin: 0 auto 10px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  padding: 5px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgba(253, 255, 254, .82);
  box-shadow: 0 5px 18px rgba(5, 50, 27, .06);
}
.investigation-tabs button {
  min-width: 0;
  min-height: 42px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: 0;
  border-radius: 10px;
  color: var(--muted);
  background: transparent;
  font-size: .86rem;
  font-weight: 850;
  cursor: pointer;
}
.investigation-tabs button span {
  width: 22px;
  height: 22px;
  display: inline-grid;
  place-items: center;
  border: 1px solid currentColor;
  border-radius: 50%;
  font-size: .68rem;
}
.investigation-tabs button[aria-selected="true"] {
  color: var(--night);
  background: var(--mint);
  box-shadow: inset 0 0 0 1px var(--mint-strong);
}
.investigation-tabs button[aria-selected="true"] span { color: var(--night); border-color: var(--green); background: var(--green); }

.laboratory-grid {
  width: min(1760px, 100%);
  margin: 0 auto;
  display: grid;
  grid-template-columns: minmax(230px, 270px) minmax(480px, 1fr) minmax(270px, 320px);
  grid-template-areas: "controls simulation evidence";
  align-items: start;
  gap: 10px;
}
.control-panel, .simulation-panel, .evidence-panel {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(253, 255, 254, .94);
  box-shadow: 0 8px 30px rgba(5, 50, 27, .07);
}
.control-panel { grid-area: controls; padding: 15px; }
.simulation-panel { grid-area: simulation; padding: 12px; }
.evidence-panel { grid-area: evidence; padding: 17px; }
.panel-heading, .simulation-toolbar, .chart-heading, .dialog-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.panel-heading h2, .simulation-toolbar h2, .investigation-copy h2, .chart-heading h3, .dialog-heading h2 {
  margin: 2px 0 0;
  color: var(--night);
  line-height: 1.17;
  letter-spacing: -.025em;
}
.panel-heading h2 { font-size: 1.02rem; }
.icon-only-button {
  width: 38px;
  height: 38px;
  flex: 0 0 auto;
  padding: 0;
  border-radius: 10px;
  font-size: 1.5rem;
}
.transport-controls { display: grid; grid-template-columns: 1fr 1fr; gap: 7px; margin: 13px 0; }
.control-stack { display: grid; gap: 10px; }
.range-control { display: grid; gap: 5px; }
.range-control > span { display: flex; justify-content: space-between; gap: 8px; font-size: .8rem; }
.range-control b { color: var(--night); }
.range-control output { color: var(--green-dark); font-weight: 850; font-variant-numeric: tabular-nums; }
.range-control small { color: var(--muted); font-size: .68rem; line-height: 1.32; }
input[type="range"] {
  width: 100%;
  height: 5px;
  margin: 4px 0;
  border-radius: 99px;
  accent-color: var(--green-dark);
  cursor: pointer;
}
.switch-control {
  display: flex;
  align-items: center;
  gap: 9px;
  margin: 13px 0;
  color: var(--night);
  font-size: .8rem;
  cursor: pointer;
}
.switch-control input { position: absolute; opacity: 0; pointer-events: none; }
.switch-control > span {
  position: relative;
  width: 38px;
  height: 22px;
  flex: 0 0 auto;
  border: 1px solid var(--line);
  border-radius: 99px;
  background: #dce9e2;
  transition: background-color .16s ease;
}
.switch-control > span::after {
  content: "";
  position: absolute;
  top: 3px;
  left: 3px;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  background: var(--paper);
  box-shadow: 0 1px 4px rgba(5, 50, 27, .2);
  transition: transform .16s ease;
}
.switch-control input:checked + span { background: var(--green); border-color: var(--green-dark); }
.switch-control input:checked + span::after { transform: translateX(16px); }
.switch-control input:focus-visible + span { outline: 3px solid var(--green-dark); outline-offset: 3px; }
.comparison-controls { padding-top: 12px; border-top: 1px solid var(--line); }
.comparison-controls > div { display: grid; grid-template-columns: 1fr 1fr; gap: 6px; margin: 7px 0; }
.comparison-controls p { min-height: 34px; margin: 0; color: var(--muted); font-size: .7rem; }

/* Simulation ---------------------------------------------------------- */
.simulation-toolbar { min-height: 52px; padding: 1px 3px 9px; align-items: flex-end; }
.simulation-toolbar h2 { font-size: 1.05rem; }
.live-readouts { display: flex; justify-content: flex-end; gap: 5px; flex-wrap: wrap; }
.live-readouts > span {
  min-width: 88px;
  display: grid;
  padding: 5px 9px;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--cream);
}
.live-readouts small { color: var(--muted); font-size: .61rem; font-weight: 750; }
.live-readouts b { color: var(--night); font-size: .76rem; font-variant-numeric: tabular-nums; }
.microscope-frame {
  position: relative;
  min-height: clamp(390px, 64svh, 720px);
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--paper);
  box-shadow: inset 0 0 0 7px rgba(244, 251, 247, .82);
}
.lab-screen[data-mode="einstein"] .microscope-frame { min-height: clamp(260px, 36svh, 390px); }
#particle-canvas, #msd-canvas { display: block; width: 100%; height: 100%; }
#particle-canvas { position: absolute; inset: 0; }
.scale-bar {
  position: absolute;
  left: 19px;
  bottom: 18px;
  display: grid;
  gap: 3px;
  color: var(--night);
  font-size: .65rem;
  font-weight: 850;
}
.scale-bar span { display: block; width: 68px; height: 3px; background: var(--night); }
.view-key {
  position: absolute;
  right: 14px;
  bottom: 13px;
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 8px;
  max-width: calc(100% - 110px);
}
.view-key span {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 4px 7px;
  border: 1px solid rgba(212, 233, 221, .9);
  border-radius: 8px;
  color: var(--muted);
  background: rgba(253, 255, 254, .88);
  font-size: .62rem;
  font-weight: 750;
  backdrop-filter: blur(7px);
}
.view-key i { display: block; border-radius: 50%; }
.tracer-key { width: 11px; height: 11px; border: 2px solid var(--night); background: var(--green); }
.molecule-key { width: 7px; height: 7px; background: var(--green-dark); }
.canvas-action {
  position: absolute;
  top: 13px;
  right: 13px;
  min-height: 36px;
  color: var(--green-dark);
  border-color: var(--mint-strong);
  background: rgba(253, 255, 254, .92);
  font-size: .72rem;
  backdrop-filter: blur(7px);
}
.canvas-action:hover { background: var(--mint); }

.einstein-chart-area { padding: 11px 3px 2px; }
.chart-heading h3 { font-size: .95rem; }
.equation-chip {
  padding: 5px 9px;
  border: 1px solid var(--mint-strong);
  border-radius: 999px;
  color: var(--green-dark);
  background: var(--mint);
  font-size: .7rem;
  font-weight: 850;
  white-space: nowrap;
}
#msd-canvas {
  height: 210px;
  margin-top: 7px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--paper);
}
.chart-values { display: flex; flex-wrap: wrap; gap: 7px 15px; margin-top: 6px; color: var(--muted); font-size: .7rem; }
.chart-values b { color: var(--night); font-variant-numeric: tabular-nums; }

/* Evidence ------------------------------------------------------------ */
.investigation-copy h2 { margin-bottom: 8px; font-size: 1.15rem; }
.investigation-copy > p { margin: 0 0 12px; color: var(--muted); font-size: .84rem; }
.thinking-prompt {
  margin: 12px 0;
  padding: 12px;
  border-left: 3px solid var(--green);
  border-radius: 0 10px 10px 0;
  background: var(--cream);
}
.thinking-prompt span { color: var(--green-dark); font-size: .66rem; font-weight: 900; letter-spacing: .08em; text-transform: uppercase; }
.thinking-prompt p { margin: 3px 0 0; color: var(--night); font-size: .8rem; font-weight: 650; }
.observation-inference { display: grid; gap: 7px; margin: 0; }
.observation-inference div { padding: 9px 10px; border: 1px solid var(--line); border-radius: 10px; }
.observation-inference dt { color: var(--green-dark); font-size: .68rem; font-weight: 900; text-transform: uppercase; letter-spacing: .07em; }
.observation-inference dd { margin: 3px 0 0; color: var(--muted); font-size: .76rem; }
.impact-meter { display: grid; gap: 5px; margin: 12px 0; }
.impact-meter > span { display: flex; justify-content: space-between; color: var(--muted); font-size: .72rem; }
.impact-meter > div { position: relative; height: 8px; overflow: hidden; border-radius: 99px; background: linear-gradient(90deg, #bdebd2 0 50%, #def5e9 50%); }
.impact-meter i { position: absolute; top: 0; left: 50%; width: 4px; height: 100%; border-radius: 99px; background: var(--night); transform: translateX(-50%); transition: left .16s ease; }
.relationship-list { display: grid; gap: 7px; margin: 12px 0; }
.relationship-list span { display: grid; grid-template-columns: auto 1fr auto; align-items: center; gap: 8px; color: var(--night); font-size: .78rem; }
.relationship-list i { height: 1px; background: var(--line); }
.relationship-list strong { color: var(--green-dark); }
.equation-block { display: grid; justify-items: center; gap: 3px; margin: 12px 0; padding: 12px; border: 1px solid var(--mint-strong); border-radius: 12px; background: var(--mint); }
.equation-block span { color: var(--muted); font-size: .68rem; }
.equation-block strong { color: var(--night); font-size: 1.12rem; letter-spacing: .02em; }
.history-timeline { display: grid; gap: 8px; margin: 13px 0 0; padding: 0; list-style: none; }
.history-timeline li { position: relative; padding-left: 18px; }
.history-timeline li::before { content: ""; position: absolute; top: 5px; left: 1px; width: 8px; height: 8px; border: 2px solid var(--green-dark); border-radius: 50%; background: var(--paper); }
.history-timeline li:not(:last-child)::after { content: ""; position: absolute; top: 15px; bottom: -10px; left: 5px; width: 1px; background: var(--line); }
.history-timeline b { display: block; color: var(--night); font-size: .72rem; }
.history-timeline span { display: block; color: var(--muted); font-size: .68rem; }
.misconception-check, .model-note { margin-top: 13px; padding-top: 11px; border-top: 1px solid var(--line); }
.misconception-check summary, .model-note summary { color: var(--night); font-size: .78rem; font-weight: 850; cursor: pointer; }
.misconception-check > p, .model-note p { margin: 8px 0; color: var(--muted); font-size: .72rem; }
.answer-options { display: grid; grid-template-columns: 1fr 1fr; gap: 6px; }
.answer-options button { min-height: 36px; padding: 6px; font-size: .7rem; }
.answer-options button.is-correct { border-color: var(--green-dark); background: var(--mint); }
.answer-options button.is-incorrect { border-color: var(--coral); background: #fff1f2; }
.answer-feedback { min-height: 31px; }

.lab-footer {
  width: min(1760px, 100%);
  margin: 8px auto 0;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 6px 18px;
  color: var(--muted);
  font-size: .67rem;
}

/* Guide dialog -------------------------------------------------------- */
dialog {
  width: min(860px, calc(100% - 30px));
  max-height: calc(100svh - 30px);
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 20px;
  color: var(--ink);
  background: var(--paper);
  box-shadow: var(--shadow);
}
dialog::backdrop { background: rgba(6, 25, 20, .42); backdrop-filter: blur(5px); }
.dialog-heading h2 { font-size: 1.35rem; }
.guide-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 9px; margin: 18px 0; }
.guide-grid article { padding: 13px; border: 1px solid var(--line); border-radius: 13px; background: var(--cream); }
.guide-grid article > span { width: 25px; height: 25px; display: grid; place-items: center; border-radius: 50%; color: var(--night); background: var(--green); font-size: .72rem; font-weight: 900; }
.guide-grid h3 { margin: 9px 0 4px; color: var(--night); font-size: .9rem; }
.guide-grid p { margin: 0; color: var(--muted); font-size: .72rem; }

@media (max-width: 1220px) {
  .laboratory-grid { grid-template-columns: minmax(220px, 250px) minmax(430px, 1fr) minmax(240px, 275px); }
  .live-readouts > span { min-width: 80px; }
  #collision-readout-wrap { display: none; }
  .header-actions a { display: none; }
}

@media (max-width: 980px) {
  .lab-header { grid-template-columns: auto 1fr; }
  .header-actions { grid-column: 1 / -1; justify-content: flex-end; margin-top: -4px; }
  .laboratory-grid {
    grid-template-columns: minmax(220px, 255px) minmax(0, 1fr);
    grid-template-areas:
      "simulation simulation"
      "controls evidence";
  }
  .microscope-frame { min-height: min(58svh, 600px); }
  .guide-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 720px) {
  .lab-screen { padding-inline: 8px; }
  .lab-header { gap: 10px; }
  .lab-heading .eyebrow { display: none; }
  .lab-heading h1 { font-size: 1rem; }
  .lab-brand img { height: 25px; }
  .header-actions { display: none; }
  .investigation-tabs { overflow-x: auto; grid-template-columns: repeat(4, minmax(126px, 1fr)); justify-content: start; scrollbar-width: thin; }
  .investigation-tabs button { font-size: .76rem; }
  .laboratory-grid { grid-template-columns: 1fr; grid-template-areas: "simulation" "controls" "evidence"; }
  .control-panel, .simulation-panel, .evidence-panel { border-radius: 14px; }
  .microscope-frame { min-height: 52svh; }
  .simulation-toolbar { align-items: flex-start; }
  .live-readouts > span { min-width: 0; }
  .live-readouts > span:first-child { display: none; }
  .control-stack { grid-template-columns: 1fr 1fr; column-gap: 14px; }
  .comparison-controls, .switch-control, .transport-controls, .panel-heading { grid-column: 1 / -1; }
  .lab-footer { padding: 0 8px; }
}

@media (max-width: 520px) {
  .entry-brand { left: 12px; }
  .entry-pause { right: 12px; }
  .entry-pause span { display: none; }
  .entry-pause { width: 42px; padding: 0; }
  .lab-header { grid-template-columns: auto minmax(0, 1fr); }
  .lab-heading h1 { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
  .investigation-tabs {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    overflow: visible;
  }
  .investigation-tabs button { min-height: 38px; }
  .simulation-panel { padding: 8px; }
  .simulation-toolbar { display: grid; }
  .live-readouts { justify-content: flex-start; }
  .microscope-frame { min-height: 48svh; }
  .lab-screen[data-mode="einstein"] .microscope-frame { min-height: 270px; }
  .canvas-action { top: 9px; right: 9px; }
  .control-stack { grid-template-columns: 1fr; }
  .guide-grid { grid-template-columns: 1fr; }
  dialog { padding: 17px; }
  .chart-heading { align-items: flex-start; }
  .equation-chip { font-size: .63rem; }
  #msd-canvas { height: 190px; }
}

@media (max-width: 390px) {
  .lab-brand { padding-inline: 8px; }
  .lab-brand img { max-width: 116px; }
  .lab-heading h1 { font-size: .91rem; }
  .simulation-toolbar h2 { font-size: .96rem; }
  .live-readouts b { font-size: .69rem; }
  .view-key { display: none; }
  .scale-bar { left: 14px; bottom: 14px; }
  .answer-options { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    scroll-behavior: auto !important;
    transition-duration: .01ms !important;
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
  }
}