:root{
  --cell-size: 120px;
  --cell-gutter: 20px;
}


#grid{
  width: calc((var(--cell-size) + var(--cell-gutter)) * 3);
  height: calc((var(--cell-size) + var(--cell-gutter)) * 3);
  
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;

  align-content: space-between;
  justify-content: space-between;
}

.cell{
  height: var(--cell-size);
  width: var(--cell-size);
  border: 4px solid #ffffff;

  cursor: pointer;

  font-size: 60px;
  display: flex;
  align-items:center;
  justify-content: center;
}