.box {
  width: 50px;
  height: 50px;
  position: absolute;
  line-height: 50px;
  text-align: center;
  border: 1px solid lightgrey;
}

.empty {
  background-color: darkgrey;
  text-indent: -99999999999px;
}

.filled {
  background-color: teal;
  color: lightgoldenrodyellow;
}

#puzzle {
  position: relative;
  margin-bottom: 100px;
}

.hidden {
  visibility: hidden;
}

#message {
  color: red;
}