#score{
    text-align: center;
}

h2 {
    text-align: center;
}

div{
    margin: 0 auto;
    width: 100px;
    height: 100px;
}

#main {
    width: 400px;
    height: 400px;
    background: white;
    border: 2px solid gray;
    margin: 0 auto;
    position: relative;
    overflow: hidden;
}

#con {
    width: 100%;
    height: 400px;
    position: relative;
    top: -100px;
    border-collapse:collapse;
}

.row{
    height: 100px;
    width: 100%;}

.cell{
    height: 100px;
    width: 100px;
    float: left;}

@media screen and (max-width: 639px) {
    #main{
        width: 100%;
    }

    .cell{
        width:calc(100% /4 - 4px /4) ;
    }

}

.black {
    background: black;
}


aside{
    position: relative;
    margin: 0 auto;
    display: flex;
    justify-content: center;
    margin-top: 20px;
}

h2{
    display: inline-block;
}

#start{
    display: inline-block;
}