gtk-style-hc: Improve HighContrast border styling
This fixes the borders of the app context bar and the .content-box
class so they use the same border colour as the GTK HighContrast theme,
and so the border is defined in the right place in the app context bar
hierarchy.
Signed-off-by: Philip Withnall pwithnall@endlessos.org
Fixes: #1303 (closed)
Closes #1303 (closed)