Comment 7 for bug 1447995

I've added a darker background that becomes visible when the overflow panel is visible.
This seems to make clearer to which delegate the panel is related.

However we may want in future to add an arrow pointing to the tile, although it would require a bit more of work, since this is not currently allowed by the UITK when the popover uses a squared style.

Because of this, I look forward for your reply, and I'll eventually consider to open a separate bug report with a lower priority for updating to the following design advices.