Uniform theme and fonts for Qt apps in GTK environments

_{By @joekamprad}

There are many ways to get a uniform look and feel working, and here we show only one or two solutions.

QGnomePlatform

The easiest way to set a uniform appearance for QT applications under GTK environments is using QGnomePlatform

Sources are marked unmaintained: https://github.com/FedoraQt/QGnomePlatform#qgnomeplatform-project-is-unmaintained-a-no-longer-actively-developed as of August 2023.

But still simply possible to build and install from AUR:

yay -Syu qgnomeplatform-qt5 qgnomeplatform-qt6

This will bring in adwaita-qt5 adwaita-qt6 can be replaced with other themes that supports both gtk and qt these two will use adwaita (default gtk theme) and making qt apps following adwaita dark and light theme.

( per example breeze and breeze-gtk will work too)

Add the environment variable either systemwide at /etc/environment or user specific into a ~/.config/environment.d/envvars.conf file or ~/.profile depending on the used Desktop or WM setup it could be zthe one or the other needs to be used.

QT_QPA_PLATFORMTHEME=gnome

Note: this variable is set per default for Gnome and if you are using Gnome you do not need to set the vatriable.

After a reboot qt apps should use adwaita same as set for gtk in settings.

To set font sice and some opther setting qt5ct and qt6ct will come in handy: sudo pacman -Syu qt5ct qt6ct

qt5/6ct gui let you set theming for qt apps per example set adwaita dark if it does not apply per default..

Kvantum:

Another way will be to use Kvantum and QT5/6CT:

Install both packages:

sudo pacman -Syu kvantum qt5ct qt6ct

Both applications are required because kvantum does not allow the font settings. Therefore qt5ct is also set as an environment variable, as it works in most desktop environments or when using a window manager as a user. In some cases, e.g. when using Cinnamon, it is necessary to set the variable system-wide, because Cinnamon seems to ignore variables that are set as users. Then we set qt5ct to use the kvantum theme and set fonts inside qt5ct.

Per-user variable will be configured like so:

It seems this method is not working on XFCE4 where using ~/.profile usage is working!

Same counts for Cinnamon.

Create the needed directory

mkdir ~/.config/environment.d

and the needed config file with the needed variable:

echo "QT_QPA_PLATFORMTHEME=qt5ct" > ~/.config/environment.d/qt-theme.conf

To use ~/.profile method:

echo "export QT_QPA_PLATFORMTHEME=qt5ct" >> ~/.profile

To set this systemwide (if per user variable does not work at all):

su

echo "QT_QPA_PLATFORMTHEME=qt5ct" >> /etc/environment