body {
    font-family: sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #f0f0f0;
}

.grid-container {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-gap: 10px;
    margin-top: 20px;
}

.card {
    width: 100px;
    height: 140px;
    perspective: 1000px;
    cursor: pointer;
}

.card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

.card.flipped .card-inner {
    transform: rotateY(180deg);
}

.card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    -webkit-backface-visibility: hidden;
    backface-visibility: hidden;
    border-radius: 5px;
}

.card-front {
    background-color: #007bff;
    color: white;
}

.card-back {
    background-color: white;
    color: black;
    transform: rotateY(180deg);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 40px;
}