scroll-neg-z-index-and-composited-child.html

<!doctype HTML>
<style>
body {
  margin: 0;
}
::-webkit-scrollbar {
  display: none;
}
#scroller {
  background: gray;
  height: 300px;
  overflow: scroll;
  position: relative;
  z-index: 0;
}

#content {
  overflow: hidden;
  position: relative;
  background-color: white;
  width: 1000px;
  height: 1000px;
  top: 50px;
}
</style>
<!-- The test succeeds if white is visible across all of the visible scrolling area, and no gray -->
<div id="scroller">
  <div id="content"></div>
  <div style="position: relative; z-index: -1; will-change: transform"></div>
</div>
<script>
onload = function() {
  scroller.scrollTop = 50;
}
</script>

chromium/third_party/blink/web_tests/compositing/overflow/scroll-neg-z-index-and-composited-child.html