Update Breeze Dark Look and Feel theme previews
Summary:
Update and improve some old Breeze Dark Look and Feel theme previews (similar to D18681).
Test Plan: Open the Look and Feel KCM.
Reviewers: Plasma, VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: ngraham, VDG, plasma-devel, Plasma
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D18682