/* Mobile first: the layout is a single column that a phone can show
   without horizontal scrolling, and every control is a thumb-sized
   target. Wider viewports get the canvas and the controls side by
   side. */
:root {
  color-scheme: dark;
  --bg: #0d1017;
  --panel: #161b25;
  --line: #273041;
  --ink: #e6ebf5;
  --muted: #97a3b8;
  --accent: #6ea8fe;
  --closed: #f0a05a;
  --tap: 44px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", sans-serif;
  padding: env(safe-area-inset-top) env(safe-area-inset-right)
    env(safe-area-inset-bottom) env(safe-area-inset-left);
}

header {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.6rem 1rem;
  border-bottom: 1px solid var(--line);
}

header h1 {
  font-size: 1.1rem;
  margin: 0;
  font-weight: 600;
}

.brand {
  display: flex;
  min-width: var(--tap);
  min-height: var(--tap);
  align-items: center;
}

main {
  padding: 1rem;
  max-width: 1100px;
  margin: 0 auto;
}

#stage {
  position: relative;
  background: #0a0d13;
  border: 1px solid var(--line);
  border-radius: 12px;
  overflow: hidden;
  /* Tall enough to read on a phone, capped so it never pushes the
     controls off a short viewport. */
  height: min(58vh, 460px);
  touch-action: none; /* the canvas handles its own gestures */
}

#view {
  width: 100%;
  height: 100%;
  display: block;
}

#loading {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  margin: 0;
  color: var(--muted);
}

#readout {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem 1rem;
  padding: 0.7rem 0.2rem;
  color: var(--muted);
  font-size: 0.92rem;
}

#readout b {
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}

fieldset {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  margin: 0 0 0.8rem;
  padding: 0.8rem;
}

legend {
  color: var(--muted);
  font-size: 0.85rem;
  padding: 0 0.4rem;
}

.stairbuttons,
.row {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.5rem;
}

.row {
  grid-template-columns: repeat(3, 1fr);
}

button {
  min-height: var(--tap);
  padding: 0.5rem 0.6rem;
  border-radius: 10px;
  border: 1px solid var(--line);
  background: #1e2533;
  color: var(--ink);
  font: inherit;
  font-size: 0.95rem;
  cursor: pointer;
}

button:active {
  transform: translateY(1px);
}

button.stair[aria-pressed="true"] {
  border-color: var(--closed);
  color: var(--closed);
  background: #2a2016;
}

.slider {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 0.2rem 0.6rem;
  margin-top: 0.7rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.slider input {
  grid-column: 1 / -1;
  width: 100%;
  height: var(--tap);
  accent-color: var(--accent);
}

.slider output {
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}

.hint {
  color: var(--muted);
  font-size: 0.85rem;
  margin: 0.6rem 0 0;
}

#about {
  border-top: 1px solid var(--line);
  margin-top: 1.2rem;
  padding-top: 1rem;
  color: var(--muted);
}

#about h2 {
  font-size: 1rem;
  color: var(--ink);
}

a {
  color: var(--accent);
}

@media (min-width: 900px) {
  main {
    display: grid;
    grid-template-columns: minmax(0, 1fr) 320px;
    grid-template-areas:
      "stage controls"
      "readout controls"
      "about about";
    gap: 0 1.2rem;
  }

  #stage {
    grid-area: stage;
    height: 62vh;
  }

  #readout {
    grid-area: readout;
  }

  #controls {
    grid-area: controls;
  }

  #about {
    grid-area: about;
  }
}