body{
    height: 100%;
    width: 100%;
    font-family: 'Roboto', sans-serif;
    background-image: url("https://stepik.org/media/attachments/lesson/374893/world.png");
    background-size: cover;
    background-repeat: no-repeat;
}
.quiz-area{
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
}
.title{
    flex-basis: 100%;
    text-align: center;
}
.cards-container{
    width: 660px;
    height: 660px;
    display: flex;
    flex-flow: row wrap;
    justify-content: space-around;
    text-align: center;
    font-size: 28px;
    font-weight: bold;
}
.card{
    width: 200px;
    height: 200px;
    position: relative;
}
.front,
.back{
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    border-radius: 10px;
    position: absolute;
}
.front{
    background-color: bisque;
    color: coral;
    z-index: 2;
}
.back{
    background-color: coral;
    color: bisque;
    z-index: 1;
    visibility: hidden;
}
.card:hover .back{
    visibility: visible;
}
.card:hover .front{
    visibility: hidden;
}