Timm Bäder authored Jul 08, 2017 and Matthias Clasen committed Jul 19, 2017

Remove the special case in gtkwidget.c where we didn't draw any css
background/border for popovers. Instead, rely on themes to not style the
popover node and add a contents gizmo that gets the actual css styling.
We then requeste enough space for the popover to draw both the contents
and the arrow on the side.