>> and push the two sets of buttons to either side.


If you are looking to left and right align some buttons you can use a Gtk::ButtonBox/HButtonBox (like LivePathEffects does)
// button1 will be right aligned, button2 left aligned
set_layout (Gtk::BUTTONBOX_END);
add( button1 );
add( button2 );
set_child_secondary( button2 , true);