GtkStyleContext stores styling information affecting a widget.

In order to construct the final style information, GtkStyleContext queries information from all attached GtkStyleProviders. Style providers can be either attached explicitly to the context through gtk_style_context_add_provider(), or to the display through gtk_style_context_add_provider_for_display(). The resulting style is a combination of all providers’ information in priority order.

For GTK widgets, any GtkStyleContext returned by gtk_widget_get_style_context() will already have a GdkDisplay and RTL/LTR information set. The style context will also be updated automatically if any of these settings change on the widget.

Style Classes

Widgets can add style classes to their context, which can be used to associate different styles by class. The documentation for individual widgets lists which style classes it uses itself, and which style classes may be added by applications to affect their appearance.

Custom styling in UI libraries and applications

If you are developing a library with custom widgets that render differently than standard components, you may need to add a GtkStyleProvider yourself with the GTK_STYLE_PROVIDER_PRIORITY_FALLBACK priority, either a GtkCssProvider or a custom object implementing the GtkStyleProvider interface. This way themes may still attempt to style your UI elements in a different way if needed so.

If you are using custom styling on an applications, you probably want then to make your style information prevail to the theme’s, so you must use a GtkStyleProvider with the GTK_STYLE_PROVIDER_PRIORITY_APPLICATION priority, keep in mind that the user settings in XDG_CONFIG_HOME/gtk-4.0/gtk.css will still take precedence over your changes, as it uses the GTK_STYLE_PROVIDER_PRIORITY_USER priority.