.button {
  width: 100px;
  height: 50px;
  position: relative;
  perspective: 800px;
}

.button__front,
  .button__back {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  font-weight: bold;
  text-transform: uppercase;
  color: #fff;
  background-color: #3498db;
  border-radius: 5px;
  position: absolute;
  backface-visibility: hidden;
  transition: transform 0.5s ease;
}

.button__back {
  background-color: #e74c3c;
  transform: rotateY(180deg);
}

.button:hover .button__front {
  transform: rotateY(-180deg);
}

.button:hover .button__back {
  transform: rotateY(0);
}