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

body {
    height: 100vh;
    display: flex;
    background-color: rgb(188, 248, 228);
}

.memory-game {
    height: 640px;
    width: 640px;
    margin: auto;
    display: flex;
    flex-wrap: wrap;
    perspective: 1000px;
}

.card {
    height: calc( 33.333% - 10px);
    width: calc(25% - 10px);
    margin: 5px;
    position: relative;
    box-shadow: 1px 1px 1px rgba(0,0,0,.3);
    cursor: pointer;
    transform: scale(1);
    transform-style: preserve-3d; 
    transition: transform .9s; 
}

.card:active{
    transform: scale(0.97);
    transition: transform .2s;
}

.card-front,
.card-back {
  width: 100%;
  height: 100%;
  padding: 20px;
  position: absolute;
  border-radius: 5px;
  background: rgb(92, 187, 182);
  backface-visibility: hidden; 
}

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

/* flip card animation */

.card.flip {
    transform: rotateY(180deg);
}