Hep with Subscribe to Calendar Button CSS

My site is in dev mode, so I can’t add a public link here. I have a question that is pretty basic though. I am setting all my styling to make elements work on a black site background. I have everything sorted out, but I can’t find the style that control the hover state on the “Subscribe to Calendar” button. I have the button white with black text, and I just want the hover state to stay the same. White button, black text. (basically making it so that there is no change of colour on hover).

I found a couple of old support posts but the solutions don’t quite match and aren’t very current. I couldn’t isolate the classes from them.

Thanks!