"object" plus / minus button icon is not centered

[ptitFicus]

Example (you must toggle object display to see it) : https://maif.github.io/react-forms/?schema=N4IgdghgtgpiBcoAuBPADneIDOSBOAlmAOYgA0IANhAEYyULjRwVrUDGMAFgPaUAmMPIwCaPAK54ABJFggAvhQjFMydJnDiodYRWp0GWMZKnK4ikOx6CEajIx40AVjHZIF8oA