overflow-scroll-background-opaque-to-transparent.html

<!DOCTYPE html>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<script>
onload = function() {
    runAfterLayoutAndPaint(function() {
        scroller.style.background = "transparent local content-box";
    }, true);
}
</script>
<style>
#scroller {
    background: red local content-box;
    border: 10px solid rgba(0, 255, 0, 0.5);
    contain: paint;
    overflow: scroll;
    width: 200px;
    height: 200px;
}
.spacer {
    height: 300px;
}
</style>
<div id="scroller"><div class="spacer"></div></div>
<p>Scroller background should be white</p>

chromium/third_party/blink/web_tests/compositing/overflow/overflow-scroll-background-opaque-to-transparent.html