<!DOCTYPE html>
<style>
    #elm::after { display:block; -webkit-column-span:all; background:yellow; content:".........."; }
</style>
<p>There should be two rectangles with identical sizes below. The first one should be blue
    with nothing inside. The second one should be yellow with some dots inside.</p>
<div style="-webkit-columns:4; orphans:1; widows:1; line-height:100px; background:blue;">
    <span id="elm">&nbsp;</span>
</div>