body {
  background-color: #aca;
  text-align: center;
  color: #335;
  user-select: none;
}

.cell {
  cursor: pointer;
  display: inline-block;
  width: 18%;
  margin: 5px;
  background-color: #eef;
  border-color: #aac;
  border-style: solid;
  border-radius: 15px;
  transition: opacity 0.1s linear;
}

.cell:not(.empty):hover {
  background-color: #ccd;
  transform: rotate(-2deg);
}

.cell.empty {
  opacity: 0.3;
  transition: opacity 0.3s linear;
}

.cell.empty:hover {
  opacity: 0.5;
  transform: rotate(-2deg);
  background-color: #ded;
  transition: opacity 0.3s linear;
}