body {
    height: 100vh;
    display: flex;
    flex-direction: column;
    background-color:  #60C322;
}

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

.attribution {
    margin-left: 10px;
}

.card {
    height: calc( 33.333% - 10px);
    width: calc(25% - 10px);
    margin: 5px;
    position: relative;
    box-shadow: 1px 1px 1px rgba(1, 1, 1, 0.3);
    cursor: pointer;
    transform: scale(1);
    transform-style: preserve-3d;
    transition: transform .9s ;
}

.card:active {
    transform: scale(0.97);
    transition: 0.3s;
}

.card-face, 
.card-cover {
    width: 100%;
    height: 100%;
    padding: 20px;
    position: absolute;
    border-radius: 5px;
    background-color: #fff;
    backface-visibility: hidden;
}

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

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

.hide {
    opacity: 0;
    transition: 6s;
}