body {
  font-family: sans-serif;
  text-align: center;
}

#grid {
  display: grid;
  grid-template-columns: repeat(6, 60px);
  grid-template-rows: repeat(6, 60px);
  gap: 5px;
  justify-content: center;
  margin-top: 20px;
}

.cell {
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: black;
  color: white;
  font-size: 24px;
  font-weight: bold;
  border: 2px solid #444;
  cursor: pointer;
}

.selected {
  background-color: red !important;
}

.empty {
  background-color: white;
  color: transparent;
}