view-blending-base-background.html | Explore in Territory

<!DOCTYPE html>
<script>
onload = function() {
  if (window.testRunner && window.internals)
    testRunner.setCustomTextOutput(internals.layerTreeAsText(document));
}
</script>
<body style="background: rgba(0, 0, 128, 0.5)">
  The view's background should blend the white base background and <body>'s background.
</body>

chromium/third_party/blink/web_tests/compositing/background-color/view-blending-base-background.html