gtk:widget-override-font (widget desc)

widget -- a gtk:widget object
desc -- a pango:font-description instance to use, or nil to undo the effect of previous calls

Sets the font to use for a widget. All other style values are left untouched. See the gtk:widget-override-color function. The gtk:widget-override-font function has been deprecated since version 3.16 and should not be used in newly written code. This function is not useful in the context of CSS based rendering. If you wish to change the font a widget uses to render its text you should use a custom CSS style, through an application specific style provider and a CSS style class.