<!DOCTYPE html>
<script>
if (window.internals)
  internals.useMockOverlayScrollbars();
</script>
<div style="position: relative; width: 200px; height: 200px; overflow: scroll">
  <!-- the intermediate div doesn't have layout overflow. -->
  <div style="position: relative; width: 210px; height: 80px; overflow: scroll">
    <div style="position: absolute; z-index: 5; background: green; width: 200px; height: 70px"></div>
  </div>
  <div style="height: 210px"></div>
</div>