body {
  background-color: lightblue;
  text-align: center;
  font-family: sans-serif;
  color: blue;
}

button {
  background-color: gold;
  font-size: 4rem;
  margin: 1rem;
  border: 0;
  color: blue;
  width: 6rem;
  height: 6rem;
}

button:hover {
  background-color: yellow;
}

.square, .blank, .movable, .finished {
  height: 5rem;
  width: 5rem;
  line-height: 5rem;
  margin: 0.2rem;
  font-size: 4rem;
  color: lightblue;
}

.square, .movable {
  background-color: red;
}

.blank {
  background-color: lightblue;
  color: lightblue;
}

.finished {
  background-color: green;
}

.movable:hover {
  background-color: darkred;
}

.puzzle {
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.row {
  display: flex;
  flex-direction: row;
  justify-content: center;
}