Per application dark theme

Customization
1

I am using the ZorinBlue-Light theme during the day, and ZorinBlue-Dark during the night. But for some apps it makes sense that they're always in dark mode, because they have a dark UI, like Spotify or GIMP.

On ZorinOS 17 I could do this by modifying the flatpak application environment variable "GTK_THEME=ZorinBlue-Dark" and it would do the job. On ZorinOS 18 this no longer works. Any idea on how to get dark theme only for certain applications? Thanks!

2

Hi and welcome.

Brave A.i. search using Ubuntu 24.04 in search criteria as Zorin 18 is a fork of same gives:

" To apply a dark theme to individual applications without affecting the global theme in Ubuntu 24.04, use the GTK_THEME environment variable when launching the application.

Per-Application Launch via Command Line

Set the GTK_THEME variable to load a specific theme variant (e.g., Adwaita:dark ) only for that app:

GTK_THEME=Adwaita:dark gedit

This applies the dark theme to only that instance of the application and does not change the system-wide theme.

Persistent Setup via Desktop Entry (Recommended)

To make this apply every time you launch the app:

  1. Copy the app’s .desktop file from /usr/share/applications/ to ~/.local/share/applications/ .
  2. Edit the file and modify the Exec= line to prepend env GTK_THEME=Adwaita:dark :
Exec=env GTK_THEME=Adwaita:dark /usr/bin/gedit %F
  1. Save and close the file. The app will now launch with the dark theme every time, regardless of the global theme.

:warning: Note : This method works best for GTK 3 and GTK 4 applications. Some apps (like newer versions of GNOME Terminal) may ignore GTK_THEME due to internal theming logic. For such cases, use dedicated settings (e.g., gsettings set org.gnome.Terminal.Legacy.Settings theme-variant 'dark' ).

Alternative: Dynamic Theme Enforcement

For a more automated approach, use a script that monitors window classes and applies dark themes dynamically:

  • Use tools like xprop , xdotool , and wmctrl to detect and modify window properties on the fly.
  • Example: Run a script that sets _GTK_THEME_VARIANT=dark for specific apps (e.g., Spotify, VLC) when they open.

:white_check_mark: Tip : If you're using a non-GNOME desktop (like MATE or XFCE), ensure gnome-tweaks is installed and use it to manage per-application themes safely.

AI-generated answer. Please verify critical facts."

Change the entries that state Adwaita to your preferred theme.