overlay-transition-out-rendering.html

<!DOCTYPE html>
<title>CSS Positioned Layout Module Test: 'overlay' transitioning out still rendered in top layer</title>
<link rel="help" href="https://drafts.csswg.org/css-position-4/#overlay">
<link rel="help" href="https://html.spec.whatwg.org/multipage/popover.html">
<link rel="match" href="green-ref.html">
<style>
  #green, #red {
    /* Force display:block both popover open or closed to not rely on
       @starting-style or display transitions. */
    display: block;
    border: none;
    width: 100vw;
    height: 100vh;
  }
  #red {
    background-color: red;
  }
  #green {
    background-color: green;
  }
  #green.transition-enabled {
    transition: overlay 60s step-end;
    transition-behavior: allow-discrete;
  }
</style>
<div id="red" popover="manual"></div>
<div id="green" popover="manual"></div>
<script>
  red.showPopover();
  green.showPopover();
  document.body.offsetTop;
  green.className = "transition-enabled";
  green.hidePopover();
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-position/overlay/overlay-transition-out-rendering.html