style.css

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

body {
    height: 100vh;
    background-color: black;
}

.msg{
    color: white;
    font-size: 42px;
    text-align: center;
    display: wrap;
    padding: 20px;
}

.resetButton{
    text-align: center;
    padding-top: 20px;
}

.buttonStyle{
    font-size: 24px;
    color: white;
    padding: 20px;
    background-color: rgb(58, 53, 53);
}

#cardboard{
    width: 740px;
    height: 740px;
    margin: auto;
    display: flex;
    flex-wrap: wrap;
}

.memory-card{
    width: calc(25% - 10px);
    height: 33%;
    margin: 5px;
    position: relative;
    transform-style: preserve-3d;
    transition: 0.3s;
}

.memory-card:active{
    transform: scale(0.97);
}

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

.front-face, .back-face{
    width: 100%;
    height: 100%;
    background-color: black;
    position: absolute;
    padding: 20px;
}

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