Theming support through a simplgui::Theme class giving the recommended sizes for margins, paddings and text and the recommended colors.
simplgui::Theme : stores theme informations like font name, size, colors
simplgui::StateDepProperty : store a property that depend of the widget's state (normal, focused...)
simplgui::ResourcesGetter : a generic interface for SimplGUI to get resources like textures, fonts...
simplgui::FileResourcesGetter : inherits from simplgui::ResourcesGetter and allows widgets to load resources from files (considering resources names are their filepaths)
simplgui::Renderer : an interface that allows widgets to draw themselves (needing a Theme and resources)