html {
    font-family: Arial sans-serif;
}
body {
    background: url("images/world.png") no-repeat;
    background-size: 90%;
}
.flex-container {
    display: flex;
    justify-content: center;
}
.quiz-area {

}
.card-container {
    display: flex;
    width: 350px;
    height: 350px;
    padding: 10px;
    flex-wrap: wrap;
    justify-content: space-evenly;
    align-items: center;
    background-color: pink;
    border-radius: 20px;
}
.cards {
    position: relative;
    width: 100px;
    height: 100px;
    transition: 1s;
    transform-style: preserve-3d;
    text-align: center;
}
.cards:hover {
    transform: rotateY(180deg);
}
.front, .back {
    position: absolute;
    backface-visibility: hidden;
    width: 100%;
    height: 100%;
    border-radius: 10px;
}
.front {
    background-color: #f9efe5;
}
.back {
    transform: rotateY(180deg);
    background-color: darkorange;
    color: #f9efe5;
    top: 0;
    left: 0;
}