AI to optimise CSS mess

Hi everyone,
just thought about optimising my CSS. I've got some WordPress sites with nice looking themes. But for search engines it seemed to be a mess. Double CSS, hidden or unused Css, I have a huge custom css too for better looking woocommerce and so on.

Any recommendations how I could eliminate all CSS errors without crashing the site after every theme update?
Maybe using AI to analyse the web page? I'm not an expert but making Websites responsiv isn't a problem for me. But I'm worried about how to start.
Maybe there is a simple tool or free Plugin? Somebody with experience here?

Thanks