.simon-board {
  width: min(320px, 80vw);
  height: min(320px, 80vw);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: 1fr 1fr;
  gap: 10px;
}
.pad {
  border: none;
  border-radius: 16px;
  cursor: pointer;
  opacity: .55;
  transition: opacity .12s, transform .08s;
  box-shadow: 0 4px 10px rgba(0,0,0,.15);
}
.pad:active { transform: scale(.97); }
.pad.p0 { background: #22c55e; }
.pad.p1 { background: #ef4444; }
.pad.p2 { background: #3b82f6; }
.pad.p3 { background: #eab308; }
.pad.lit { opacity: 1; box-shadow: 0 0 22px currentColor; }
.pad.p0.lit { color: #22c55e; }
.pad.p1.lit { color: #ef4444; }
.pad.p2.lit { color: #3b82f6; }
.pad.p3.lit { color: #eab308; }