td {
    font-size: 20px;
    color: black;
    cursor: pointer;
    border:2px solid black;
    padding:1px;
    width:  32px;
    height: 32px;
    text-align: center;
}  
table{
    border: 0px;
    /* margin:1px;
    padding:1px; */
    border-collapse:collapse;
    margin: auto;
    /* position: absolute;
    top:0;left:0;bottom:0;right: 0;; */
} 
.unknow{
    background: grey;
}
.highlight{
    background: silver;
}
.flag{
    background: red;
}
.know{
    background: white;
}
.mine{
    color: yellow;
    background: red;
}