Weird double shadow on GTK3

[m.rick@…]

With GTK3 applications, there are artefacts around the menus. There are double shadows.

It is not a MacPorts related issue because it has been reported in Linux as well. ​https://github.com/chjj/compton/issues/189

But it happens in at least 2 ports in MacPorts, Gnumeric and Glom, with the default theme or any other. And the problem, it makes it more difficult to use the menus especially with the contextual menus.

They give a working solution
shadow-exclude = [ "_GTK_FRAME_EXTENTS@:c" ];
But i don't know where to place it, I tried in settings.ini and the gtk.css main script inside the theme itself and none is working.

I put screen shots from Glom and Gnumeric.

[m.rick@…]

Glom menu

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Gnumeric

[m.rick@…]

Gnumeric