I’m using a column view in GTK4 (gtkmm4). One of the columns is a C++ class inheriting from a Gtk::Grid and packs a couple of buttons. The buttons are set to have some standard icons to make the UI intuitive.

One issue I have the grid is very obvious due to the buttons having a clear frame around the embedded icons.

How can I make the buttons ONLY show the icon and not show the gray-contrast area around it?