css/css-transforms/3d-rendering-context-and-fixpos.html

<!DOCTYPE HTML>
<title>CSS Test (Transforms): 3D Rendering Context following DOM Tree (fixed positioning)</title>
<link rel="author" title="L. David Baron" href="https://dbaron.org/">
<link rel="author" title="Google" href="http://www.google.com/">
<link rel="help" href="https://drafts.csswg.org/css-transforms-2/#3d-rendering-contexts">
<meta name="assert" content="Fixed positioned elements participate in 3D Rendering Contexts based on their parent, not their containing block.">
<link rel="match" href="reference/green.html">

<style>

div {
  width: 100px;
  height: 100px;
}

.cb {
  transform-style: preserve-3d;
  transform: translateX(0);
  background: red;
  position: relative;
}

.parent {
}

.abspos {
  position: fixed;
  top: 0;
  left: 0;
  /* Since this element is not in the 3D Rendering Context, this translation
     does not put it above the <div class="sibling">. */
  transform: translateZ(20px);
  background: red;
}

.sibling {
  position: absolute;
  top: 0;
  left: 0;
  transform: translateZ(10px);
  background: green;
}

</style>

<p>Pass if there is NO red below:</p>

<div class="cb">
  <div class="parent">
    <div class="abspos">
    </div>
  </div>
  <div class="sibling">
  </div>
</div>