How to style GtkButton with CSS

1. create

GtkBox

to add widgets to window;
2. create the

GtkButton

and add to the layout box with

GtkBox::pack_start

;
3. create

GtkCssProvider

;
4. load css data with

GtkCssProvider::load_from_data

;
5. create

GtkStyleContext

and add provider to the screen, to css be accessible for all widgets;