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

h1 {
    text-align: center;
    margin: 5px auto;
    font-family: cursive;
    color: greenyellow;
}

body {
    height: 100vh;
    background-image: linear-gradient(#0056d6, #0091e3, #00bac8, #9dd9be, #f1f6e5);
}

.card-game {
    width: 600px;
    height: 600px;
    margin: auto;
    display: flex;
    flex-wrap: wrap;
    border: 2px solid lime;
    perspective: 1000px;
}

.memory-card {
    width: 25%;
    height: 25%;
    position: relative;
    border: 2px solid aqua;
    transform: scale(1);
    transform-style: preserve-3d;
    transition: transform .5s;
}

.memory-card:active {
    transform: scale(0.95);
    transition: transform .2s;
}

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

.front,
.back {
    width: 100%;
    height: 100%;
    padding: 15px;
    position: absolute;
    border: 2px solid black;
    border-radius: 5px;
    background: rgb(69, 69, 247);
    backface-visibility: hidden;
}

.back {
    transform: rotateY(180deg);
}