.departure-board {
  display: inline-flex;
  flex-wrap: nowrap;
}

.letter {
  display: inline-block;
  position: relative;
  height: 60px;
  perspective: 600px;
  min-width: 0;
}

.letter span {
  display: block;
  position: absolute;
  width: 100%;
  height: 100%;
  text-align: center;
  line-height: 60px;
  font-weight: bold;
  border: 1px solid #333;
  backface-visibility: hidden;
  transform-style: preserve-3d;
}

.letter .front {
  transform: rotateX(0deg);
  z-index: 2;
}

.letter .back {
  transform: rotateX(180deg);
}

.letter.flip .front {
  transform: rotateX(180deg);
  transition: transform 0.6s ease-in-out;
}

.letter.flip .back {
  transform: rotateX(0deg);
  transition: transform 0.6s ease-in-out;
}