Overlay property instead of style

Overlaying the whole style with sw720dp will override dark theme styles.
Let's instead define the attribute that needs to be different and put it
in a config xml.

Test: set smallest width to 720, flip to dark theme
Fixes: 180003967
Change-Id: I423f3401b612e7e87a63f3f14f972b9d863d8a17
1 file changed