ormed, anywhere in the document, by:
     - An element with an opacity value less than 1.
     - An element with a will-change value specifying any property that would create a Backdrop Root on non-initial value. -->
<div class=container>
  <div class=testcase>
    <div style="opacity: 0.8;"><div></div></div>
  </div>
  <div class=testcase>
    <div style="will-change:opacity;"><div></div></div>
  </div>
</div>
