chromium/third_party/blink/web_tests/external/wpt/css/filter-effects/backdrop-filter-edge-behavior.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>backdrop-filter: Edge behavior</title>
<link rel="author" href="mailto:[email protected]">
<link rel="help" href="https://drafts.fxtf.org/filter-effects-2/#BackdropFilterProperty">
<link rel="help" href="https://crbug.com/1165868">
<link rel="match"  href="backdrop-filter-edge-behavior-ref.html">

<div>
  <p>Expected: The black box inside the red box should not contain any red.</p>
</div>

<div id=scroller>
  <div class=filler></div>
  <div id=backdrop></div>
  <div class=filler></div>
</div>

<style>
  #scroller {
    width: 250px;
    height: 250px;
    overflow: scroll;
    border: 6px solid red;
  }
  #scroller::-webkit-scrollbar {
    width: 0px;
  }
  #backdrop {
    height: 200px;
    width: 200px;
    backdrop-filter: blur(10px);
    border: 1px solid black;
  }
  .filler {
    position: relative;
    left: 50px;
    width: 100px;
    height: 100px;
  }
</style>

<script>
  scroller.scrollTop = 103;
</script>