How to Create Custom UI Themes in GIMP

Creating a custom user interface theme for GIMP allows you to tailor the software's visual appearance to match your workflow and aesthetic preferences. This guide outlines the end-to-end process of developing a GIMP theme, which includes locating the built-in theme assets, duplicating a base template into your user configuration directory, editing CSS style rules to alter interface colors and elements, and activating the new theme within GIMP’s preferences.

Step 1: Locate the Default Theme Directory

GIMP ships with several default themes (such as Dark, Light, Gray, and System). To avoid breaking system files, you should always copy an existing theme rather than editing the defaults directly.

Default installation paths:

• Windows: C:\Program Files\GIMP 2\share\gimp\2.0\themes\
• macOS: /Applications/GIMP.app/Contents/Resources/share/gimp/2.0/themes/
• Linux: /usr/share/gimp/2.0/themes/

Choose a base theme folder (for example, Dark or Light) that is closest to your target design.

Step 2: Copy the Theme to the User Directory

Copy the selected theme folder into your personal GIMP user configuration directory:

• Windows: %APPDATA%\GIMP\2.10\themes\
• macOS: ~/Library/Application Support/GIMP/2.10/themes/
• Linux: ~/.config/GIMP/2.10/themes/

Rename the copied folder to your desired custom theme name (e.g., MyCustomTheme).

Step 3: Edit the Theme Files

Inside your newly created theme folder, you will find theme configuration files, primarily gimp.css (or gtkrc in older GIMP versions). Open gimp.css in a standard text editor.

You can modify standard GTK CSS properties to change the UI styling:

• Background Colors: Change @define-color bg-color or #gimp-toolbox-window rules to alter the primary workspace tone.
• Text Colors: Modify @define-color fg-color to adjust general UI text readability.
• Selection and Highlights: Edit @define-color selected_bg_color to control active menu items, selected layers, and button states.
• Font Sizes and Padding: Adjust font-size, padding, and margin values within widget declarations to make tools more compact or spacious.

Save your changes once the modifications are complete.

Step 4: Apply and Test the Theme

1. Open or restart GIMP.
2. Navigate to Edit > Preferences (on macOS, GIMP > Preferences).
3. In the left panel, select Interface > Theme.
4. Your new theme folder name will appear in the list. Click on it to apply the theme instantly.
5. Click OK to save the preference.

If you need to make further adjustments, you can edit the gimp.css file while GIMP is open, then re-select the theme in Preferences to refresh the visual changes.