<!doctype html>
<html lang=en>
  <meta charset=utf-8>
  <title>CSS-contain test reference</title>
  <link rel="author" title="Florian Rivoal" href="https://florian.rivoal.net">
<style>
article {
  columns: 2 1ch;
  column-gap: 0;
  float: left;
  font-family: monospace;
  margin-right: 3em;
  line-height: 1;
  height: 4em;
  column-fill: auto;
}
div:last-of-type {
  break-before: column;
}
</style>

<p>Test passes if there are two identical blocks “A” letters below.
<article>
  <div>A<br>A</div>
  <div>A<br>A</div>
</article>
<article>
  <div>A<br>A</div>
  <div>A<br>A</div>
</article>