The problem with the PurifyCSS approach, like so many before it, is that you cannot really do this accurately from the server. It has to be done in the browser.
Helium is a dev tool. It takes a list of sample urls from the developer because its presumed the engineer will be able to make the best choice as to pages that represent all the aspects of their site.
It will work in any web page regardless of framework, because ultimately its all just web pages.
Helium will find the actual style sheets loaded into each page, then at the end of the scan give you an accurate and realistic report of the css selectors that were not found anywhere in your site.
There are some minor limitations, such as the inability to test for user-interactions with pseudo selectors like :active, :focus, :hover, etc.