*{
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}
body{
  height: 100vh;
  display: flex;
  background: #061AB2;
}
img{
  width: 100px;
}
.memory-game{
  width: 640px;
  height: 640px;
  margin: auto;
  display: flex;
  flex-wrap: wrap;
  perspective: 1000px;
}
.memory-card{
  width: calc(25% - 10px);
  height: calc(33.33% - 10px);
  margin: 5px;
  position: relative;
  transform: scale(1);
  transform-style: preserve-3d;
  transition: transform .5s;
}
.memory-card:active{
  transform: scale(.97);
  transition: transform .2s;
}
.memory-card.flip{
  transform: rotateY(180deg);
}
.front-face,
.back-face{
  width: 100%;
  height: 100%;
  padding: 20px;
  position: absolute;
  border-radius: 5px;
  background: #1e7ccc;
  backface-visibility: hidden;
}
.front-face{
  transform: rotateY(180deg);
}