System Settings > Desktop Appearance > Window Decoration (blank).
I clicked on “Get New Decorations…” button then installed some of decorations already but they didn’t show in decoration list at all (still blank).So I can’t change window decoration now.
Any suggestion is welcome :)[/align]
This is a known bug in Plasma 5, and only happens the first time you enter that KCM module, once you come out of it and go back in the decorations will now display properly.
Thanks to AJSlye,
Now problem was solved.