#game-container {
    width: 100%;
    height: 100vh;
    margin: 0 auto;
    display: flex;
    justify-content: center;
    align-items: center;
}

.card {
    width: 30%;
    height: 30%;
    margin: 10px;
    border: 1px solid #ddd;
    border-radius: 10px;
    cursor: pointer;
    background-color: #f0f0f0;
}

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

.card.matched {
    background-color: #dff0d8;
    border: 1px solid #3e8e41;
}