silverstripe-docsviewer/css/utilities.css

.clear { 
    clear: both;
    display: block;
    overflow: hidden;
    visibility: hidden;
    width: 0;
    height: 0;
}

.clearfix:after {
    clear: both;
    content:' ';
    display: block;
    font-size: 0;
    line-height: 0;
    visibility: hidden;
    width: 0;
    height: 0
}

* html .clearfix,
*:first-child+html .clearfix{
    zoom: 1;
}