Reconsider using a shadow as separator in NavigationTabBar, either by default, or at all
This thing:
This style isn't used in most other KDE apps, where we instead separate things with single-pixel lines. You can see the visual inconsistency in the screenshot above where the footer casts a shadow on the scrollable view above it, but the header doesn't cast a shadow on the scrollable view below it. Visually speaking, this implies either that the footer has greater height than the header, or else a lighting model where things are lit from below, which is odd and inconsistent with the lighting model we use for our buttons.
The shadow is being disabled or made to fall back to a line separator instead for its implementations in NeoChat, KClock, Koko, and the upcoming QML Powerdevil KCM (see plasma/powerdevil!259 (comment 794618)).
Let's reconsider it.