Description
According to the cssom-view-1 spec, offsetParent should expose a containing element within an open shadow tree, however, on testing it seems that chrome, firefox and safari skip the shadow tree entirely.
If ancestor is not closed-shadow-hidden from the element and satisfies at least one of the following, terminate this algorithm and return ancestor.
See https://jsbin.com/negusux/edit?html,js,output
In particular, I think the offsetParent of <DIV id="openInnerElement" class="target"> should be the .shadow-scroller element in the <open-component> if browsers were following the spec, however every browser returns the same <DIV id="outerScroller" class="scroller"> for both the open and closed shadow trees, skipping the shadow tree entirely.
I propose we update the spec to match what browsers do, skipping elements from inner shadow trees, for both offsetParent and the new scrollParent.
@tabatkins FYI