<!DOCTYPE html>
<script>
    onload = function() {
        document.body.offsetTop;
        document.getElementById('elm').style.height = '0';
    }
</script>
<p>There should be a blue <em>square</em> below.</p>
<div style="-webkit-columns:3; -webkit-column-gap:0; width:9em; line-height:9em; background:blue;">
    <div style="-webkit-column-span:all; background:black;">
        <div id="elm" style="height:15em;"></div>
    </div>
    <br>
</div>