style.css

*{
    box-sizing: border-box;
}
div.board{
    background: gainsboro;
    border: 1px solid blue;
    max-width: 1030px;
    height: auto;
    padding: 20px;
    margin: 0px auto;
    perspective: 1000px;
    display: flex;
    flex-wrap: wrap;
}
div.board>div{
    border: 1px solid black;
    border-radius: 10px;
    width: 12.1%;
    height: 120px;
    float: left;
    margin: 5px 10px;
    cursor:pointer;
    box-shadow: 3px 3px 0 rgba(0, 0, 255, .4);
    transform: scale(1);
    position: relative;
    transform-style: preserve-3d;
    transition: transform 1s;
}

.front-face,.back-face{
    width: 100%;
    height: 100%;
    position: absolute;
    border-radius: 10px;
}
.card:hover {
    transform: scale(0.97);
    transition: transform .2s;
}
.front-face {
    transform: rotateY(180deg);
}
.card.is-flipped {
    transform: rotateY(180deg);
}
.header{
    border: 1px solid black;
    background: maroon;
    border-radius: 10px;
    width: 99%;
    height: 65px;
    float: left;
    margin: 10px 1px 10px 10px;
    cursor:pointer;
    box-shadow: 3px 3px 0 rgba(0, 0, 0, .4);
    transform: scale(1);
    position: relative;
    transform-style: preserve-3d;
    transition: transform 1s;
}
@keyframes shake {
    0% { transform: translate(1px, 1px) rotate(0deg); }
    10% { transform: translate(-1px, -2px) rotate(-1deg); }
    20% { transform: translate(-3px, 0px) rotate(1deg); }
    30% { transform: translate(3px, 2px) rotate(0deg); }
    40% { transform: translate(1px, -1px) rotate(1deg); }
    50% { transform: translate(-1px, 2px) rotate(-1deg); }
    60% { transform: translate(-3px, 1px) rotate(0deg); }
    70% { transform: translate(3px, 1px) rotate(-1deg); }
    80% { transform: translate(-1px, -1px) rotate(1deg); }
    90% { transform: translate(1px, 2px) rotate(0deg); }
    100% { transform: translate(1px, -2px) rotate(-1deg); }
}
.moves{
    border: 5px solid black;
    width: 18%;
    height: 62px;
    color: white;
    background: black;
    border-radius: 10px;
    text-align: center;
    font-size: 20rem;
    float: left;
}
.gameOver{
    width: 40%;
    height:300px;
    border: 5px solid black;
    border-radius: 10px;
    color: white;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: maroon;
    -moz-backface-visibility: hidden;
}