:root {
  --bg: #f4f1ec;
  --card: #ffffff;
  --ink: #1a1a1a;
  --muted: #6b6560;
  --line: rgba(0, 0, 0, 0.08);
  --accent: #2c6bed;
  --accent-soft: rgba(44, 107, 237, 0.12);
  --ok: #1a7f4b;
  --shadow: 0 18px 48px rgba(30, 28, 24, 0.10), 0 2px 8px rgba(30, 28, 24, 0.06);
  --radius: 20px;
  font-family: system-ui, -apple-system, "SF Pro Text", "PingFang SC", "Noto Sans SC", sans-serif;
}

* { box-sizing: border-box; }
html, body {
  margin: 0; padding: 0;
  background: var(--bg);
  color: var(--ink);
  min-height: 100%;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 20px 16px 40px;
}

.shell {
  width: min(860px, 100%);
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.top {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 0 4px;
}

.kicker {
  font-size: 12px;
  letter-spacing: 0.04em;
  color: var(--muted);
  text-transform: none;
}

h1 {
  margin: 0;
  font-size: clamp(20px, 4.5vw, 26px);
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.25;
}

.eli5 {
  margin: 0;
  font-size: 14px;
  color: var(--muted);
  line-height: 1.45;
  max-width: 42em;
}

.stage-card {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border: 1px solid var(--line);
  overflow: hidden;
  position: relative;
}

.stage-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 16px 0;
  font-size: 12px;
  color: var(--muted);
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 500;
  font-size: 11px;
}

.badge.done {
  background: rgba(26, 127, 75, 0.12);
  color: var(--ok);
}

#stage {
  width: 100%;
  height: min(520px, 72vw);
  min-height: 320px;
  display: block;
  touch-action: none;
  cursor: grab;
  background:
    radial-gradient(120% 80% at 50% 30%, #fff 0%, #f7f4ef 55%, #efebe4 100%);
  user-select: none;
}
#stage:active { cursor: grabbing; }
#stage.dragging { cursor: grabbing; }

.hint-pill {
  position: absolute;
  left: 50%;
  bottom: 14px;
  transform: translateX(-50%);
  padding: 8px 14px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.88);
  border: 1px solid var(--line);
  font-size: 12px;
  color: var(--muted);
  pointer-events: none;
  backdrop-filter: blur(8px);
  transition: opacity 0.35s ease;
}
.hint-pill.hide { opacity: 0; }

.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  padding: 4px;
}

.btn {
  appearance: none;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--ink);
  border-radius: 12px;
  padding: 10px 14px;
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  box-shadow: 0 1px 2px rgba(0,0,0,0.04);
  transition: background 0.15s ease, transform 0.1s ease;
}
.btn:hover { background: #fafafa; }
.btn:active { transform: scale(0.98); }
.btn.primary {
  background: var(--ink);
  color: #fff;
  border-color: var(--ink);
}
.btn.primary:hover { background: #333; }
.btn.on {
  background: var(--accent-soft);
  border-color: rgba(44, 107, 237, 0.35);
  color: var(--accent);
}

.slider-wrap {
  display: flex;
  align-items: center;
  gap: 10px;
  flex: 1 1 180px;
  min-width: 160px;
  padding: 0 4px;
}
.slider-wrap label {
  font-size: 12px;
  color: var(--muted);
  white-space: nowrap;
}
input[type="range"] {
  flex: 1;
  accent-color: var(--accent);
}

.readout {
  font-variant-numeric: tabular-nums;
  font-size: 12px;
  color: var(--muted);
  padding: 8px 12px;
  border-radius: 10px;
  background: rgba(0,0,0,0.03);
  border: 1px solid var(--line);
}

.foot {
  font-size: 11px;
  color: var(--muted);
  line-height: 1.5;
  padding: 0 4px;
}
.foot a { color: var(--muted); }

@media (max-width: 420px) {
  body { padding: 14px 10px 28px; }
  #stage { height: 58vh; min-height: 300px; }
  .controls { gap: 8px; }
  .btn { padding: 9px 12px; font-size: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  .hint-pill { transition: none; }
  .btn { transition: none; }
}

.btn.ghost {
  background: transparent;
  border-color: var(--line);
  color: var(--muted);
  box-shadow: none;
  padding: 8px 12px;
  font-size: 12px;
}
.btn.ghost:hover { background: rgba(0,0,0,0.03); color: var(--ink); }

.lock-steps {
  padding-top: 0;
}

#stage.grab-key { cursor: ew-resize; }
#stage.grab-turn { cursor: grab; }

@media (max-width: 420px) {
  .lock-steps .btn.ghost { padding: 8px 10px; }
  .lock-steps { gap: 6px; }
}