nested-scroll-overlay-scrollbar.html

<!DOCTYPE html>
<script>
if (window.internals)
  internals.useMockOverlayScrollbars();
</script>
<div style="width: 200px; height: 200px; overflow: scroll">
  <!-- The intermediate div doesn't have layout overflow. -->
  <div style="height: 210px; overflow: scroll">
    <div style="background: green; width: 300px; height: 100px"></div>
  </div>
</div>

chromium/third_party/blink/web_tests/scrollbars/nested-scroll-overlay-scrollbar.html