Apps built with QT (aka KDE apps) do not look great on the XFCE 4 desktop because they don’t respect the default theme. The way to fix this is to use Kvantum. With Kvantum, you can set KDE app themes to use a similar theme to what you use in XFCE 4.
Before we begin
In this guide, we’ll be using the Adapta GTK theme for XFCE. We’re focusing on Adapta because it has a Kvantum theme that is widely available and helps blend KDE apps in with XFCE 4 quite well.
Before starting this guide, we highly recommend installing the Adapta GTK theme onto your Linux PC and enabling it as the default theme in XFCE. For information on how to set up Adapta, click here.
Installing Kvantum on Linux
To get Kvantum working on your Linux PC, you will need to install it alongside the management tool. To get started, open up a terminal window and install the Kvantum manager, as well as everything else necessary to use it.
On Ubuntu, you can get the Kvantum tools on your system via the Papirus PPA. This PPA has everything you need to get it working. To add the PPA, use the following add-apt-repository command.
sudo add-apt-repository ppa:papirus/papirus
After adding the Papirus PPA to your Linux PC, run the update command to refresh your software sources.
sudo apt update
Finally, use the apt install command below to get the Kvantum packages to use the Kvantum theme engine on Ubuntu.
sudo apt install qt5-style-kvantum qt5-style-kvantum-themes
On Debian 11 and 10, the Kvantum packages should be available for installation without any need to add a third-party software repository to your computer. To get it working, open up a terminal window and enter the command below.
sudo apt-get install qt5-style-kvantum qt5-style-kvantum-themes
Kvantum is available to Arch Linux users and has been for a very long time. There is an AUR package. There’s also a package in the official Arch Linux software sources, which we recommend.
To get the latest Kvantum on your Arch Linux PC, enter the following terminal command.
sudo pacman -S kvantum-qt5
On Fedora Linux, you can get the latest Kvantum on your PC with the following Dnf command. There is no need to add any third-party software repositories, as they’re inside the official software sources.
sudo dnf install kvantum
Kvantum is available to OpenSUSE users via a third-party software repository. To start the installation, you must add the repo with the command below.
sudo zypper ar obs://home:trmdi trmdi
After adding the software repo, you can install the latest version of Kvantum on your OpenSUSE PC using the zypper command below.
sudo zypper in -r trmdi kvantum
Downloading Kvantum themes
In this guide, we’re focusing on the Kvantum Adapta theme. However, if you want to use a different GTK theme and need a matching Kvantum theme to go with it, the best place to go is the KDE Store.
The KDE Store has tons of stuff to download, including Kvantum theme engine themes. To download a Kvantum theme, head over to the Kvantum page on the KDE store. From there, look through the latest themes to download.
Once you’ve downloaded a theme, launch Kvantum Manager, select “Install/Update Theme,” and install it. Then, select “Change/Delete Theme” to start using it on your system.
Using Kvantum to make KDE apps look better
To make your KDE apps look better on the XFCE 4 desktop, start by launching “Kvantum Manager” from the app menu. If you cannot find it in the app menu, open up the XFCE 4 quick launcher with Alt + F2, and enter “kvantummanager” in the launch box.
Once the Kvantum Manager app is open on the XFCE 4 desktop, follow the step-by-step instructions outlined below.
Step 1: Locate the “Change/Delete Theme” option in the Kvantum Manager. If you cannot find it, it is directly below the “Install/Update Theme.”
After selecting the “Change/Delete Theme” button, you will see a menu that says “Select a theme,” followed by a blank text box. Change it to “Kvdapta.”
Step 2: Open up a terminal window and install the Qt5ct app.
sudo apt install qt5ct
sudo apt-get install qt5ct
sudo pacman -S qt5ct
sudo dnf install qt5ct
sudo zypper install qt5ct
Step 3: Open up a terminal window and use the echo command to edit the profile file to add the environmental variable.
echo "export QT_QPA_PLATFORMTHEME=qt5ct" >> ~/.profile
Step 4: Log out of your XFCE 4 session and log back in.
Step 5: Open up Qt5ct via the app menu. Or, launch it via the terminal with the qt5ct command.
Step 6: Locate the “Appearance” tab. Then, find the “Style” menu. In the menu, select “kvantum.” Then, select “Apply” to apply changes.
Upon applying your changes, KDE applications on XFCE 4 should be using the Kvantum theme set up earlier.