.grid {

    width: 1024px;

    height: 1024px;

    font-size: 1rem;

}

.row {

    display: flex;

}

.box {

    background: rgb(220, 0, 0);

    width: 20px;

    height: 20px;

    margin: 0px;

    color: white;

    flex: 1 0 auto;

    position: relative;

}

.box:after {

    content: "";

    float:left;

    display: block;

    padding-top: 100%;

}

.box .inner {

    position: absolute;

    left: 0;

    right: 0;

    bottom: 0;

    top: 0;

    display: flex;

    align-items: center;

    justify-content: center;

}



#id{

    background: blue;

}