Use Header colors in PlasmoidHeading headers
This brings applets with distinct heading areas into visual consistency with windows, once the Tools Area MR lands.
When using a color scheme that lacks Header colors, there is no visual change whatsoever. But here's how it looks when you are using a color scheme with header colors (note: this is a WIP color scheme and the final shade of gray may be different):
In Kickoff:
In the System Tray grid:
In Plasma-nm:
In the clock:
The full effect:
cc @teams/vdg