Fix the look of KDE apps in other desktop environments

The problem

Ever re-installed your OS but kept your /home partition and got to experience some weird visual artifacts? If your desktop environment is XFCE for instance and your KDE apps (such as okular, konsole, spectacle or gwenview) look bad, then you’d normally solve this with Kvantum Manager. Kvantum is used for styling Qt apps. It worked great out of the box for the Manjaro clean installs I’ve done so far, but the same cannot be said about the latest (re-) install where I just kept my /home partition and installed Manjaro onto a brand new SSD.

The solution

Again, out of the box, Kvantum Manager works great… until it doesn’t. I might have forgotten to install a particular Qt theme. Instead of tracking down that particular package, an alternative solution is to install qt5ct. As explained on this Arch Linux wiki page, qt5ct provides another way to style KDE apps from within a desktop environment other than KDE. So this should work for XFCE, as well as Gnome and what have you.

Just install it:

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sudo pacman -S qt5ct

Next, you need to make an environment variable available globally to specify that it is qt5ct that should be used as the Qt platform abstraction. This can be achieved by adding the following line to /etc/profile:

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export QT_QPA_PLATFORMTHEME=qt5ct

Now launch qt5ct and select the desired theme.

Log out and log in again and your KDE apps should now be better integrated visually into your non-KDE desktop environment.