Hi!
I am not sure if this is possible to be honest. I don’t think there is a way of telling if a drop-down box has changed via CSS, it is always considered as ‘selected’, since every value is a selection. I know it is possible to change the item colors somehow, but it will change all the text colors within the selection. Let me know if you have an example of this somewhere, maybe I can somehow integrate it with a bit of custom code.