[gtkmm] How to increase the size of a notebook's arrows

["Ohrnberger, Erik" <erik_ohrnberger dme net>]

In a Gtk::Notebook, when there are more pages than hose tabs can be
displayed, the Notebook displays two arrows that allows the user to scroll
the displayed tabs back and forth to reveal the hidden tabs.

Is there a way to make these arrows, or more properly triangles, larger?

	Thanks,
		Erik.