root-element-background-transparency-ref.html

<!doctype HTML>
<title>Backround color transparency on the root element blends with a white backdrop</title>
<link rel="author" title="Chris Harrelson" href="mailto:[email protected]">
<link rel="help" href="https://drafts.fxtf.org/compositing/#pagebackdrop">
<html style="background: rgb(150, 150, 150)">
  <div id=spacer style="width: 100px; height: 3000px"></div>
</html>

chromium/third_party/blink/web_tests/external/wpt/css/compositing/root-element-background-transparency-ref.html