I have no idea how half the editor controls work (on Desktop). How do you assign colors to a button? There's no 'accept' action in the color picker, 'X' closes

I have no idea how half the editor controls work (on Desktop). How do you assign colors to a button? There's no 'accept' action in the color picker, 'X' closes it without assigning the color, and clicking on the color rectangle changes it randomly on mouse over, before you can apply it. Is this supposed to be mobile only?