<!DOCTYPE html>
<p>Test adding a ::before pseudo element. The DOM element is preceded by content.</p>
<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="line-height:100px; background:blue;">
    <br>
    <div style="background:yellow;">..........</div>
    <br>
</div>