body {
  font-family: sans-serif;
  text-align: center;
}
#board {
  display: grid;
  grid-template-columns: repeat(8, 40px);
  grid-template-rows: repeat(8, 40px);
  gap: 2px;
  margin: 20px auto;
  width: fit-content;
}
.cell {
  width: 40px;
  height: 40px;
  background-color: green;
  border-radius: 4px;
  cursor: pointer;
}
.cell.black::after, .cell.white::after {
  content: '';
  width: 30px;
  height: 30px;
  border-radius: 50%;
  display: block;
  margin: auto;
}
.cell.black::after { background: black; }
.cell.white::after { background: white; }