Using 18.04.
The class is called GtkCheckButton and this really looks like adwaita to me


I wondered if this is a gnome-music specific issue and tried to find some other checkboxes, didn't find any yet. In gnome-todo they use a different element class GtkEventBox which you themed allready


@Feichtmeier First of all, excellent music collection! :musical_note: Thanks for reporting this issue!
I searched for the checkbox in the gtk3.0 folder and there are only the adwaita checkbox assets.
But you allready got assets for the checkbox in the gtk2 folder - maybe you can use those?
I wonder how GtkEventBox is themed. Can't find the class in the _common.scss
I'm seeing the green checkbuttons on my end. Are you still getting the issue?
@Feichtmeier
After selecting an object, change Miscellaneous to CSS Nodes, that'll give you the widget and class names used in the scss files.
Sadly yes, I am using the ppa on my machine, maybe something went wrong on the 17.10->18.04 upgrade past weeks. Checking on my VM where I pull the changes manually. Checked the assets folder and there is still only adwaita.
Edit: checked it now - nope it's the same on my VM (this is gnome-todo though but it uses GtkCheckButton, too):

@godlyranchdressing yes it's still present until now on both snap installation on my families computers and on my host machine with up to date master
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@Feichtmeier First of all, excellent music collection! :musical_note: Thanks for reporting this issue!