Paste CSS for AO “Inline and Defer” when using CriticalCSS Power-Up?

I’m sorry, I’ve been looking, but cannot find a clear answer to this question.

I was using basic AO that someone else set up, and they had pasted CSS into the box as directed. However, I recently upgraded to the full version PLUS the CriticalCSS power-up. So my question is: What do I do with the CSS that was already in the box?
– Do I keep the “Inline and Defer” checked?
– Do I need to replace/update the CSS that was pasted? Can/should I delete it and leave the box blank?
– Does/Did CriticalCSS replace it? Override it?

Sorry, again, I can imagine many possibilities depending on how you decided to code it. I’d really appreciate it if you could clear this up for me!

Thanks!