border-radius-composited-subframe.html

<!DOCTYPE html>
<style>
  .bordered {
    height: 150px;
    width: 250px;
    background-color: blue;
    border-style: solid;
    border-radius: 25px;
    border-width: 10px;
    border-color: gray;
    margin: 10px 10px;
  }
  .shadowed {
    box-shadow: 0 0 10px 10px;
  }
</style>
<iframe id="iframe1" class="bordered" src="resources/composited-subframe-2.html">
</iframe>
<iframe id="iframe2" class="bordered shadowed" src="resources/composited-subframe-2.html">
</iframe>

chromium/third_party/blink/web_tests/compositing/overflow/border-radius-composited-subframe.html