overflow-overlay-scrollbar-with-stacked-children.html

<!doctype html>
<style>
#scroller::-webkit-scrollbar {
  background: green;
  width: 100px;
}
#scroller {
  width: 100px;
  height: 100px;
  overflow-y: overlay;
  overflow-x: hidden;
  position: relative;
}
#notransform {
  width: 100px;
  height: 50px;
  background: red;
  position: relative;
  z-index: 1;
}
#transform {
  width: 100px;
  height: 50px;
  background: red;
  position: absolute;
  will-change: transform;
  z-index: 2;
}
</style>
<div id="scroller">
  <div id="notransform"></div>
  <div id="transform"></div>
  <div id="forcescroll" style="height: 200px; width: 10px;"></div>
</div>

chromium/third_party/blink/web_tests/scrollbars/overflow-overlay-scrollbar-with-stacked-children.html