Take a look at https://wiki.archlinux.org/index.php/qt one way is using the plugin [1], that not necessarily does a good job, but, hey, that is nowadays Linux, it's absolutely inconsistent. [1] No Rosegarden here, but Rui's apps are based upon Qt, too: [rocketmouse at archlinux ~]$ qjackctl qt5ct: using qt5ct plugin