takes your HTML and CSS as input and returns only the used CSS as output.
Not sure if this requires npm installer or if one can just download

1.3.18 beta version, still testing they say. Find unused css

tool to purge unused css. Seems to need npm or other dependency to install, though I'm not sure, and don't understand how I would use it.

only decent tip seemed to be to use 'Web page performance' in Chrome dev tools, then look for 'Remove unused CSS rules'

online tool to remove unused css from html file. Be careful - remember that css that's not used on one page, might be used on another. Seems to me that this would only be really useful on a single page site

online tool for removing unused css on a page - useful for, say, the 404 page. On the other hand, it could create a new http request