<!DOCTYPE html>
<meta charset="utf-8" />
<title>Popover ::backdrop pseudo element appearance</title>
<link rel="author" href="mailto:masonf@chromium.org">
<link rel=help href="https://open-ui.org/components/popover.research.explainer">
<link rel=help href="https://html.spec.whatwg.org/multipage/popover.html">
<link rel="match" href="popover-backdrop-appearance-ref.html">

<style>
#bottom { top: 70px; left: 70px; }
#middle { top: 120px; left: 120px; }
#top { top: 170px; left: 170px; }
::backdrop { height: 200px; width: 200px; }
#bottom::backdrop {
  top: 50px;
  left: 50px;
  background-color: rgb(0, 50, 0);
  z-index: 100;  /* z-index has no effect. */
}
#middle::backdrop {
  top: 100px;
  left: 100px;
  background-color: rgb(0, 130, 0);
  z-index: -100;  /* z-index has no effect. */
}
#top::backdrop {
  top: 150px;
  left: 150px;
  background-color: rgb(0, 210, 0);
  z-index: 0;  /* z-index has no effect. */
}
[popover] {
  margin:0;
}
</style>
<p>Test for [popover]::backdrop presence and stacking order. The test passes
  if there are 3 stacked boxes, with the brightest green on top.</p>
<div popover id=bottom>Bottom
  <div popover=hint id=middle>Middle
    <div popover=manual id=top>Top</div>
  </div>
</div>
<script>
document.getElementById('bottom').showPopover();
document.getElementById('middle').showPopover();
document.getElementById('top').showPopover();
</script>
