<div class="flip-container">
  <div class="card">
    <div class="front">
    </div>
    <div class="back">
    </div>
  </div>
</div>

body {
  background: #fcd443;
}

.flip-container {
  position: absolute;
  left: 50%;
  top: 50%;
  margin-top: -240px;
  margin-left: -320px;
  perspective:1200;
}
.flip-container:hover .card {
  transform:rotateY(-180deg);
}
.card {
  width: 640px;
  height: 480px;
  transition:all 1.2s;
  transform-style:preserve-3d;
}
.front, .back {
  width: 640px;
  height: 480px;
  position: absolute;
  top: 0px;
  left: 0px;
  backface-visibility:hidden;
}

.front {
  background: url('https://res.cloudinary.com/highflyer910/image/upload/v1565192990/es_reyvem.png');
  background-color: #323c6b;
  background-size: cover;
  z-index: 1;
}

.back {
  background: url('https://res.cloudinary.com/highflyer910/image/upload/v1565192990/a5jluq_unabhl.png');
  background-size: cover;
  background-color: #323c6b;
  z-index: 2;
  transform: rotateY(-180deg);
}