scrollToTop can't delete the :hover colour

I put a colour for the scrollToTop button when over, but realized that it’s remaining on the smartphone, which I find not nice.
So, I tried to delete it and put it just when active for the smartphone.
When I delete it the app is asking me if I’m sure, but after saving it, when I come back to :hover the colour is still there.

Any idea of how to do?