body {
    font-family: Arial, sans-serif;
    text-align: center;
}

#board {
    display: inline-grid;
    padding: 10px;
    grid-gap: 1px;
    background-color: #ccc;
}

.cell {
    width: 30px;
    height: 30px;
    background-color: #ddd;
    border: 1px solid #999;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
    cursor: pointer;
}

.cell.opened {
    background-color: #bbb;
}

.cell.mine {
    background-color: red;
    color: white;
}

.cell.flag {
    background-color: yellow;
}