Created attachment 281980 [details] simple example showing the behavior When a container element with the default static positioning contains an absolutely positioned element that overflows the static container's boundaries will not change in appearance when clicked or hovered on. only the part of the absolute element that overlaps the static element will darken. clicking on the absolute element will still trigger the brightness effect on the parent element. if you apply brightness on both :hover and :active, it will work properly. when viewing the attachment, take a look at the absolute circles. the left side (static) should behave like the right side (relative). this works as expected in chrome and firefox.
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.