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chromium/third_party/blink/web_tests/fast/multicol/span/pseudo-after-then-content.html 

<!DOCTYPE html>
<style>
    #elm::after { display:block; -webkit-column-span:all; background:yellow; content:".........."; }
</style>
<p>There should be three rectangles with identical sizes below. The first and third 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>
    &nbsp;
</div>