Qt apps look out of place on my desktop. They use a different theme and color palate to the native GTK apps.
Is there a way to get KDE/Qt5-based apps to integrate better by using the same theme as the GTK apps. If not, how can I set the theme of Qt5 apps on my gnome-based desktop?
You can install the qt5-style-plugins package from the Ubuntu repositories:
Then edit ~/.profile with a text editor. For example, using Gedit, you can open that file from a terminal using:
In this file, add the following as a new line, without removing anything from the ~/.profile file:
Next, save the file and finally logout and log in. This will make Qt5 apps use Gtk2 style, which will look better, but not perfect.
For more styles, you can try qt5ct (a PPA is available).
For Qt5 applications you can also use Kvantum, which allows using a SVG-based theme engine. It comes with built-in themes that resemble some popular Gtk themes, like Ambiance, Yaru (Communitheme), Adapta, Adwaita, and more, which makes Qt apps look a lot better. The application also allows various customizations, assign themes to specific applications, and more. For how to install Kvantum in Ubuntu, see this page.