#game-board {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-gap: 10px;
    padding: 20px;
}
.card {
    width: 100px;
    height: 100px;
    background-color: #ccc;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 24px;
    cursor: pointer;
    user-select: none;
}