Ok so I think the "selection" design is quite obvious in the stylesheet I'm asked to write the appliaction in.

And the problem is that the button is staying "selected" until I press another button, also when I'm not hovering with the mouse over it.
So from what I can see the issue is not the"pressed" but the hover/selected state.

I would expect the selected state to not last when I am not hovering over the button, clicking on the background etc.
But it gets only changed when I selected another button ui element. Is there anyway to change that behaviour?