<!DOCTYPE html>
<p>There should be a blue <em>square</em> below.</p>
<div style="-webkit-columns:3; columns:3; -webkit-column-gap:0; column-gap:0; width:300px;">
    &nbsp;
    <div style="-webkit-column-break-before:always; break-before:column; height:400px; background:blue;"></div>
    <div style="-webkit-column-span:all; column-span:all;">&nbsp;</div>
</div>