If you want to style the fonts
Code:
$.jGrowl('<div style="font-weight:normal;color:#ffffff;">{vb:raw notifications_menubits}</div> <br /><div style="font-weight:normal;color:#ffffff;">You must view your notification(s) before this box will disappear.</div>' , { sticky: true, header : '<div style="font-weight:normal;color:#ffffff;">New Notification(s)</div>' } );
Then mess around with using div styles like pictured above. To change the black/transparent bg then you will need to edit the .css file