<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS test reference</title>
<link rel="author" title="Florian Rivoal" href="https://florian.rivoal.net/">
<style>
div { white-space: pre; }
span { background: blue; }
</style>

<p>Test passes if the characters below are arranged in a square and if there is a blue rectangle at the end of the first line.
<div>ああ<span>&#x3000;&#x3000; &#x3000; &#x3000;</span><br>ああ</div>