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

<!DOCTYPE html>
<meta charset="utf-8">
<title>backdrop-filter: Edge pixels shouldn't get filtered</title>
<link rel="author" href="mailto:[email protected]">
<link rel="help" href="https://drafts.fxtf.org/filter-effects-2/#BackdropFilterProperty">
<link rel="match"  href="backdrop-filter-edge-pixels-ref.html">

<div class="box"></div>
<div style="position:absolute;top:100px;will-change:transform;">
  <p>Expected above: A pure white box with a blue border.<br>
  No dark/black should be observed within the white box.</p>
</div>

<style>
.box {
  position: absolute;
  width: 100px;
  height: 100px;
  top: 0px;
  left: 0px;
  border: 1px solid blue;
  backdrop-filter: blur(30px);
}
</style>