.sl-board {
  display: grid;
  gap: 2px;
  width: min(92vw, 360px);
  margin: 14px auto;
  user-select: none;
}
.sl-cell {
  position: relative;
  aspect-ratio: 1 / 1;
  background: #eef1f6;
  border-radius: 6px;
  cursor: pointer;
}
.sl-cell.given { background: #dde3ec; cursor: default; }
.sl-cell .ln {
  position: absolute;
  top: 50%; left: 50%;
  width: 76%; height: 4px;
  background: #2b2f38;
  border-radius: 2px;
  transform: translate(-50%, -50%) rotate(45deg);
}
.sl-cell.o0 .ln { transform: translate(-50%, -50%) rotate(-45deg); }
.sl-cell .clue {
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  width: 58%; height: 58%;
  border-radius: 50%;
  border: 2px solid #ff6b6b;
  background: rgba(255, 255, 255, 0.78);
  color: #ff6b6b;
  font-size: 12px;
  font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  z-index: 2;
}