style.css

* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

body {
  height: 100vh;
  display: flex;
  background-color: rgb(140, 0, 255);
}
.memory-game {
  width: 640px;
  margin:auto;
  display: flex;
  height: 640px;
  flex-wrap: wrap;
  perspective: 1000px;
}

.memory-card {
  width: calc(25% - 10px);
  height: (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: #1ca3cc;
  backface-visibility: hidden;
}

.front-face{
    transform: rotateY(180deg);
}