GtkThemingEngine is the object used for rendering themed content in GTK+ widgets. Even though GTK+ has a default implementation, it can be overridden in CSS files by enforcing a GtkThemingEngine object to be loaded as a module. In order to implement a theming engine, a GtkThemingEngine subclass must be created, alongside the CSS file that will reference it, the theming engine would be created as an .so library, and installed in $(gtk-modules-dir)/theming-engines/. GtkThemingEngine<!-- -->s have limited access to the object they are rendering, the GtkThemingEngine API has read-only accessors to the style information contained in the rendered object's GtkStyleContext.