body {
    font-family: Arial, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    margin: 0;
    background: #f4f4f4;
}

h1 {
    margin-bottom: 20px;
}

.game-board {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-gap: 15px;
}

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

.card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    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%;
    backface-visibility: hidden;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
}

.card-front {
    background: #333;
    color: #fff;
}

.card-back {
    background: #4caf50;
    transform: rotateY(180deg);
    color: #fff;
}