Use CSS for demo site only, not to be used in theme after selected.

My original post (Select which plugins get activated on new site) closed with no option for response. So, please allow me to respond via this post.

I fully understand that checking the box applies all active plugins to a new site. I should have been more clear by asking, “Is there a way to choose which “active” plugin will be applied to a new site?” I assume there isn’t, but I may be wrong.

What I need to do is apply CSS to the demo site only. As soon as the client signs up, selects the theme and then applies it, the CSS rules from the demo no longer exist.

I initially thought to use a CSS plugin which is only active for the demo, but doesn’t get applied to a new site once the theme is selected and in use.

Perhaps there’s another way such as using conditional statements?

I appreciate your expert advice.