def set_global_styles(self, editor_widget):
    pango_context = editor_widget.create_pango_context()
font_description = pango_context.get_font_description()
increase = 14
font_size = 1024 * increase
font_description.set_size(font_size)
editor_widget.override_font(font_description)
Атрибуты pango с pygobject