body {
  height: 100vh;
  display: flex;
  align-items: center;
}

.cards {
  width: 400px;
  margin: 0 auto;
  -webkit-perspective: 1000px;
          perspective: 1000px;
}
.cards__container {
  width: 100%;
  position: relative;
  padding-bottom: 71.5%;
  transition: 1s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  -webkit-transform-style: preserve-3d;
          transform-style: preserve-3d;
}
.cards__front, .cards__back {
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden;
          backface-visibility: hidden;
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 5px;
  background-size: cover;
  box-shadow: 25px 25px 50px rgba(0, 0, 0, 0.2);
}
.cards__front {
  z-index: 2;
  -webkit-transform: rotateY(0deg);
          transform: rotateY(0deg);
}
.cards__back {
  -webkit-transform: rotateY(180deg);
          transform: rotateY(180deg);
}
.cards.is-flipped .cards__container {
  -webkit-transform: rotateY(180deg);
          transform: rotateY(180deg);
}

.card-1 {
  background-image: url(https://source.unsplash.com/YQ3FpeQkNhA/800x600);
}

.card-2 {
  background-image: url(https://source.unsplash.com/gGC63oug3iY/800x600);
}

.card-3 {
  background-image: url(https://source.unsplash.com/PAcI-vmFL2g/800x600);
}

.card-4 {
  background-image: url(https://source.unsplash.com/_d0zgyMmYT8/800x600);
}