chromium/content/test/data/accessibility/css/reading-flow.html

<style>
.wrapper {
  display: flex;
  reading-flow: flex-visual;
}
</style>

<!--- Test reading flow for flex items re-ordered using CSS property order.
Only direct children of wrapper are re-ordered.

Expect order to be:
(div 1) -> 1  -> 2  -> 3  -> 4  -> (div 5) -> 5.1 -> 5.2 -> 6
-->

<div class="wrapper">
  <button style="order: 3">3</button>
  <div style="order: 1">
    <button>1</button>
  </div>
  <button style="order: 4">4</button>
  <button style="order: 6">6</button>
  <div style="order: 5">
    <button style="order: 2">5.1</button>
    <button style="order: 1">5.2</button>
  </div>
  <button style="order: 2">2</button>
</div>