table div {
    background-color: gray;
    width: 20px;
    height: 20px;
    text-align: center;
}

table, th, td {
    border: 1px solid black;
}

.undefined {
    background-color: gray;
}

.checked {
    background-color: yellow;
}

.no-bomb {
    background-color: white;
}

.bomb {
    background-color: red;
}

input {
    width: 40px;
}