themingengine: background applies to full border
themingengine: background applies to full border

The code was attempting to only apply it to half of the border. But
according to CSS, the background area by default is the full border box.

Adamovskiy/gtk,Adamovskiy/gtk,davidt/gtk,jadahl/gtk,davidt/gtk,chergert/gtk,chergert/gtk,bratsche/gtk-,jadahl/gtk,jigpu/gtk,jadahl/gtk,jessevdk/gtk,Distrotech/gtk2,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,Distrotech/gtk2,bratsche/gtk-,ahodesuka/gtk,jadahl/gtk,msteinert/gtk,Lyude/gtk-,jessevdk/gtk,chergert/gtk,davidt/gtk,jigpu/gtk,davidgumberg/gtk,jigpu/gtk,jigpu/gtk,alexlarsson/gtk,Lyude/gtk-,Adamovskiy/gtk,chergert/gtk,alexlarsson/gtk,Lyude/gtk-,davidgumberg/gtk,Adamovskiy/gtk,Distrotech/gtk2,Sidnioulz/SandboxGtk,grubersjoe/adwaita,davidt/gtk,jigpu/gtk,jadahl/gtk,jessevdk/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,Distrotech/gtk2,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,Lyude/gtk-,ebassi/gtk,bratsche/gtk-,Lyude/gtk-,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita,Adamovskiy/gtk,davidgumberg/gtk,Distrotech/gtk2,davidt/gtk,ahodesuka/gtk,ahodesuka/gtk,ebassi/gtk,alexlarsson/gtk,ahodesuka/gtk,davidgumberg/gtk,chergert/gtk,jessevdk/gtk,alexlarsson/gtk,alexlarsson/gtk,jadahl/gtk,Lyude/gtk-,chergert/gtk,Lyude/gtk-,ebassi/gtk,bratsche/gtk-,davidgumberg/gtk,msteinert/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jessevdk/gtk,jessevdk/gtk,alexlarsson/gtk,jessevdk/gtk,ebassi/gtk,Adamovskiy/gtk,chergert/gtk,Sidnioulz/SandboxGtk,Distrotech/gtk2,ahodesuka/gtk,Adamovskiy/gtk,bratsche/gtk-,ebassi/gtk,jigpu/gtk,jadahl/gtk,chergert/gtk,msteinert/gtk,grubersjoe/adwaita,msteinert/gtk,davidgumberg/gtk,davidgumberg/gtk,jadahl/gtk,msteinert/gtk,ahodesuka/gtk,davidt/gtk,ebassi/gtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,alexlarsson/gtk,Lyude/gtk-,msteinert/gtk,bratsche/gtk-