.sudoku-board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  aspect-ratio: 1 / 1;
  border: 4px solid var(--ink);
  background: var(--ink);
  gap: 1px;
}
.sudoku-cell {
  border: 0;
  background: var(--paper);
  color: var(--ink);
  font: inherit;
  font-size: clamp(18px, 4vw, 34px);
  font-weight: 800;
  cursor: pointer;
}
.sudoku-cell:nth-child(3n) { border-right: 3px solid var(--ink); }
.sudoku-cell:nth-child(n+19):nth-child(-n+27),
.sudoku-cell:nth-child(n+46):nth-child(-n+54) { border-bottom: 3px solid var(--ink); }
.sudoku-cell.given {
  background: color-mix(in srgb, var(--green) 16%, var(--paper));
}
.sudoku-cell.wrong {
  color: var(--red);
}
.number-pad {
  margin-top: 14px;
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}
.number-pad button {
  min-height: 42px;
  border: 0;
  border-radius: 6px;
  background: var(--green);
  color: #fff;
  font-weight: 800;
  cursor: pointer;
}