Breeze is the standard for the user but for root applications (e.g. partition manager, krusader, ...) the old oxygen style (widget style, color scheme, icons) are used. root apps should also use the breeze style. Reproducible: Always Steps to Reproduce: 1. start partition manager 2. 3.
I prepared a "fix" for this that switches kdelibs from defaulting to oxygen to defaulting to breeze https://mail.kde.org/pipermail/kde-distro-packagers/2015-October/000105.html which should make them properly use breeze by default. Unfortunately this probably isn't going to be landed since it is a rather stark behavioral change that introduces a runtime dependency on breeze, so it's probably best if distributions opt to apply the change through a patch instead.
Harald, can you choose the right bugzilla component for this
Probably breeze as it contains kde4breeze which is supposed to force cohesive default settings onto kdelibs applications. Alas, as I say I am not sure we can actually fix this proper other than changing kdelibs behavior which is undesirable for compatibility reasons. Ultimately apps run as a different user are meant to have different settings, making the behavior while unfortunate and inconsistent from a session POV a very expected and in fact intended one (i.e. we don't want root apps to write configs in a users home since the chown would be incorrect). Unless we build a bridge forcing foreign-apps to use session user settings (e.g. via a QPA that implements suitable fallbacks, and that also only would work for Qt5+) I don't see this getting fixed. There also is [1] [2] which I think is used in some distros to get pretty good session coherence. Since it is built around X11 that's pretty moot though come wayland. [1] http://standards.freedesktop.org/xsettings-spec/xsettings-spec-0.5.html [2] https://github.com/derat/xsettingsd
I vote for closing this bug, as I think currently (when Plasma5 is widely adopted) Breeze is always default including fresh (not kde4 upgrade) root account. Tested and confirmied with Debian 9/Plasma 5.8. Apps opened as root use Breeze style by default (without previous configuration of that).
Yup, this is "fixed" now. But really, you shouldn't run apps as root or use root sessions in the first place. Edmund, thanks for your bug triaging efforts! Feel free to mark these kinds of bugs as RESOLVED if they're now fixed or no longer applicable.