columns.css

div.css-columns {
    background-color: #eee;
    column-count: 2;
    column-gap: 1em;
    column-rule-style: none;
}

div.box {
    break-inside: avoid-column;
}

div.columns.left {background-color: #efe;width:49%;float:left;} 
div.columns.right {background-color: #eef;width:49%;float:right;} 

div.top2columns.top {background-color: #fee;} 
div.top2columns.left {background-color: #efe;width:49%;float:left;} 
div.top2columns.right {background-color: #eef;width:49%;float:right;} 

div.bottom2columns.left {background-color: #efe;width:49%;float:left;} 
div.bottom2columns.right {background-color: #eef;width:49%;float:right;} 
div.bottom2columns.bottom {background-color: #fee;clear:both;} 

div.centeredoverlay.back {background-color: #efe;} 
div.centeredoverlay.front {position:absolute;left:25%;width:50%;top:25%;height:50%;}