body {
    font-family: Arial, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #f0f0f0;
    margin: 0;
    padding: 20px;
}

#game-container {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-gap: 15px;
    margin-top: 20px;
}

.card {
    width: 100px;
    height: 100px;
    background-color: #4caf50;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 40px;
    color: white;
    cursor: pointer;
    border-radius: 8px;
    user-select: none;
    transition: transform 0.3s;
}

.card.flipped {
    background-color: #fff;
    color: #000;
    transform: rotateY(180deg);
}