GTK and Qt Applications

This guide covers theming applications built with GTK, Qt, and KDE Plasma toolkits.

GTK 3/4 Applications

GTK applications include most GNOME apps and many Linux applications. Noctalia can automatically theme them using the adw-gtk3 theme.

Setup

1. Install required packages:

   # Arch Linux / Manjaro
   paru -S adw-gtk-theme nwg-look
   
   # Other distributions
   # Install adw-gtk-theme and nwg-look from your package manager

2. Apply the GTK theme:

   • Using nwg-look (recommended):

     GTK4 Theming

     In nwg-look, make sure to uncheck the GTK4 option. Leaving GTK4 checked can prevent GTK4 applications from using Noctalia’s color scheme.

     If you previously applied a custom GTK4 theme, you may need to hit “Clear” (found in the Preference tab) in nwg-look before reapplying and regenerating the color scheme. This ensures the new colors are accepted by GTK4 apps.

     • Open nwg-look
     • Select adw-gtk3 from the theme list
     • Click “Apply”
     • 

• Using command line:

  gsettings set org.gnome.desktop.interface gtk-theme 'adw-gtk3'

3. Enable GTK theming in Noctalia:

• Open Settings → Templates
• Toggle on GTK

Troubleshooting

• Theme not applying: Completely restart GTK applications (close and reopen)
• Some apps still look wrong: Some GTK apps may need GTK 4 theme separately:

  gsettings set org.gnome.desktop.interface gtk-theme 'adw-gtk3'
  gsettings set org.gnome.desktop.interface color-scheme 'prefer-dark'  # or 'prefer-light'

• Flatpak apps: Flatpak apps may need the theme installed in their sandbox:

  flatpak install org.gtk.Gtk3theme.adw-gtk3-dark
  flatpak install org.gtk.Gtk3theme.adw-gtk3

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Qt Applications

Qt applications include KDE apps and many cross-platform applications. KDE apps (Dolphin, KDE Connect) require the use of a KColorScheme, and so this is the preferred way to theme QT applications. Use of a normal QT theme instead of a KColorScheme can cause colors to appear incorrectly or unreadable when running KDE apps. If KDE apps are not used, then the normal QT theme can be used instead.

Setup

1. Install an application that allows you to apply QT/KColorScheme themes: While the setup steps will go through the process of using qt6ct-kde, there are multiple options available.

   • qt6ct (qt6ct-kde with the KDE patches)

     # Arch Linux / Manjaro / CachyOS
     paru -S qt6ct-kde

   • qtengine (https://github.com/kossLAN/qtengine)
   • hyprqt6engine (https://github.com/hyprwm/hyprqt6engine)

2. Set environment variable: Add this to your window manager configuration or shell profile:

   For Niri (config.kdl):

   environment {
     QT_QPA_PLATFORMTHEME "qt6ct"
   }

   For Hyprland (hyprland.conf):

   env = QT_QPA_PLATFORMTHEME,qt6ct

   For Sway (config):

   setenv QT_QPA_PLATFORMTHEME qt6ct

   For shell profile (~/.bashrc or ~/.zshrc):

   export QT_QPA_PLATFORMTHEME=qt6ct

3. Enable the KColorScheme (or QT theme) in Noctalia:

• Open Settings → Templates
• Toggle on KColorScheme (or Qt)

4. Configure qt6ct:

• Run qt6ct from terminal
• In the Appearance tab, there will be a dropdown for “Color scheme:”
• In the dropdown select noctalia (KColorScheme) if using a KColorScheme for KDE app compatibility, or noctalia for a normal QT theme without the need for KDE app compatibility.
• Click Apply and OK

KDE File Picker

If you use the KDE file picker, go to the Settings tab in qt6ct and set Standard dialogs to KDE (note that this needs plasma-workspace to be installed to appear as a dropdown option)..

Troubleshooting

• Qt apps not themed: Ensure the environment variable is set before launching applications
• qt6ct not found: Make sure qt6ct is installed and in your PATH
• Theme not updating: Restart Qt applications after changing color schemes
• “The application is not configured correctly”: If opening qt6ct states this, it is likely that the QT_QPA_PLATFORMTHEME environment variable is not correctly set to qt6ct (Note: This may require a reboot if you set it for the first time).

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KDE Plasma (KColorScheme)

If you’re using KDE Plasma, Noctalia can apply colors through the native KColorScheme system.

Setup

1. Enable KColorScheme in Noctalia:

• Open Settings → Templates
• Toggle on KColorScheme

2. Apply in KDE System Settings:

• Open System Settings → Appearance → Colors
• Select the noctalia color scheme
• The scheme will update automatically when you change colors in Noctalia

Troubleshooting

• Scheme not appearing: Restart KDE Plasma or log out and back in
• Colors not updating: Ensure KColorScheme toggle is enabled in Noctalia settings