Doing that would definitely help trim out unused styles but you’d need to roll your own CSS for things like
- Box sizing reset
- Basic Form styling
- All root typography options like font sizes, font families, etc.
- Content/blog styling (headings, paragraphs etc.)
- Classes used to hide elements per breakpoint.
One thing you could do is run the Integrity stylesheet through a CSS prettifier (to unminify it) then carve out sections you don’t think you need. It’s quite off the beaten path so I wouldn’t recommend it as part of a site building process if you’re making several sites, but it might be worth experimenting with on one site where you’re trying to heavily optimize it.