:root {
  color-scheme: dark;
  --bg: #08111f;
  --panel: rgba(10, 20, 38, 0.9);
  --panel-2: rgba(20, 33, 58, 0.95);
  --line: rgba(255, 255, 255, 0.1);
  --text: #e8f2ff;
  --muted: #9ab2d1;
  --beam: #7ae7ff;
  --beam-2: #ccf8ff;
  --receiver: #ffc86a;
  --accent: #87ffba;
  --danger: #ff968e;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  min-height: 100vh;
  font-family: Inter, system-ui, sans-serif;
  background: radial-gradient(circle at top, #163257 0%, var(--bg) 55%);
  color: var(--text);
}
.wrap {
  width: min(100%, 760px);
  margin: 0 auto;
  padding: 20px 16px 32px;
}
.topnav, .subtitle, .message, .legend, .controls { text-align: center; }
.topnav { color: var(--muted); margin-bottom: 18px; }
.topnav a { color: var(--text); text-decoration: none; }
.hero { text-align: center; margin-bottom: 18px; }
.eyebrow { text-transform: uppercase; letter-spacing: 0.14em; color: var(--accent); font-size: 0.72rem; }
h1 { margin: 6px 0; font-size: clamp(2rem, 6vw, 3rem); }
.subtitle { color: var(--muted); max-width: 40ch; margin: 0 auto; }
.hud {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  margin: 18px 0 14px;
}
.hud > div, .legend, .board, .controls {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 18px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.18);
}
.hud > div { padding: 10px 12px; text-align: center; }
.label { display: block; color: var(--muted); font-size: 0.78rem; margin-bottom: 4px; text-transform: uppercase; letter-spacing: 0.08em; }
.legend {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 10px 16px;
  padding: 12px;
  color: var(--muted);
  margin-bottom: 14px;
}
.chip {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 999px;
  margin-right: 6px;
  vertical-align: -1px;
}
.chip.source { background: var(--beam); box-shadow: 0 0 10px var(--beam); }
.chip.receiver { background: var(--receiver); }
.chip.mirror { background: #8ba7ff; }
.chip.router { background: #ff91c2; }
.chip.splitter { background: #87ffba; }
.board {
  display: grid;
  gap: 8px;
  padding: 14px;
}
.cell {
  position: relative;
  aspect-ratio: 1;
  background: var(--panel-2);
  border-radius: 16px;
  border: 1px solid rgba(255,255,255,0.05);
  overflow: hidden;
}
.cell::before {
  content: "";
  position: absolute;
  inset: 8%;
  border-radius: 14px;
  border: 1px dashed rgba(255,255,255,0.03);
}
.cell.beam { background: linear-gradient(180deg, rgba(122,231,255,0.18), rgba(122,231,255,0.04)), var(--panel-2); }
.cell.receiver.hit { box-shadow: inset 0 0 0 2px rgba(255,200,106,0.35), 0 0 24px rgba(255,200,106,0.2); }
.piece {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  font-size: clamp(1.3rem, 4.8vw, 2rem);
  user-select: none;
}
.piece.rotatable { cursor: pointer; }
.piece.rotatable:active { transform: scale(0.96); }
.piece.source { color: var(--beam-2); text-shadow: 0 0 12px var(--beam); }
.piece.receiver { color: #ffd089; }
.piece.receiver.hit { color: #fff3c6; text-shadow: 0 0 18px rgba(255,200,106,0.9); }
.piece.mirror { color: #bdd0ff; }
.piece.router { color: #ffc0db; }
.piece.splitter { color: #baffd4; }
.segment {
  position: absolute;
  background: linear-gradient(90deg, rgba(204,248,255,0.2), rgba(122,231,255,0.92), rgba(204,248,255,0.2));
  box-shadow: 0 0 16px rgba(122,231,255,0.75);
  border-radius: 999px;
  pointer-events: none;
}
.segment.h { height: 7px; top: calc(50% - 3.5px); left: 0; right: 0; }
.segment.v { width: 7px; left: calc(50% - 3.5px); top: 0; bottom: 0; background: linear-gradient(180deg, rgba(204,248,255,0.2), rgba(122,231,255,0.92), rgba(204,248,255,0.2)); }
.controls {
  display: flex;
  gap: 10px;
  justify-content: center;
  padding: 14px;
  margin-top: 14px;
}
button {
  appearance: none;
  border: none;
  border-radius: 999px;
  padding: 12px 18px;
  background: linear-gradient(180deg, #8effc2, #53cb98);
  color: #062012;
  font: inherit;
  font-weight: 700;
}
button#nextBtn { background: linear-gradient(180deg, #8fd8ff, #5aa8ff); color: #091726; }
button:disabled { opacity: 0.45; }
.message {
  min-height: 1.6em;
  color: var(--muted);
  margin-top: 14px;
}
@media (min-width: 640px) {
  .hud { grid-template-columns: repeat(4, minmax(0, 1fr)); }
}