<!DOCTYPE html>
<style>
html {
  background: red;
  /* an "L" shape */
  clip-path: polygon(50px 50px, 100px 50px, 100px 100px, 150px 100px, 150px 150px, 50px 150px);
  will-change: transform;
}
div {
  width: 500px;
  height: 500px;
  background: green;
}
</style>
<link rel="help" href="http://www.w3.org/TR/css-masking-1/#the-clip-path">
<link rel="help" href="https://drafts.fxtf.org/compositing/#rootgroup">
<link rel="help" href="https://drafts.fxtf.org/compositing/#pagebackdrop">
<link rel="match" href="reference/clip-path-document-element-ref.html">
<meta name="assert" content="Clip-path on the document element applies to the root background.
    The test passes if there is a green 'L' shape without red.">
<div></div>