a #GtkStyleProvider
the priority of the style provider. The lower it is, the earlier it will be used in the style construction. Typically this will be in the range between %GTK_STYLE_PROVIDER_PRIORITY_FALLBACK and %GTK_STYLE_PROVIDER_PRIORITY_USER
3.0
Adds a style provider to @context, to be used in style construction. Note that a style provider added by this function only affects the style of the widget to which @context belongs. If you want to affect the style of all widgets, use gtk_style_context_add_provider_for_screen().
Note: If both priorities are the same, a #GtkStyleProvider added through this function takes precedence over another added through gtk_style_context_add_provider_for_screen().