Polish sidebar header appearance
Summary:
Polish the category headers in response to user feedback and for aesthetic reasons.
- Category page: Made the separator line always visible
- Subcategory page: Removed the redundant border lines in the back button and made the separator always visible
- Widescreen view: Made the header text bold to match other headers, and made the background gray match the search bar header that's right next to it
BUG: 392340
Test Plan:
Reviewed By: mart, Plasma, VDG
Subscribers: davidedmundson, abetts, richardbowen, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D11757