...traversal. We've already fixed step 3 and 9 to not filter out
non-positioned stacking contexts, because modern CSS has more ways to
create stacking context besides being positioned with z-index (like by
using "transform", "filter" or "clip-path" properties).
See following spec issue for more details https://github.com/w3c/csswg-drafts/issues/2717
Visual improvement on https://basecamp.com/