I've been looking for something like this, but with support for styles added using JavaScript. I have found anything yet, and it doesn't appear that this would do it either?
It also supports lists of HTML and CSS files to search through. It can perform login, find duplicates, list used rules as well as unused rules, as well as count how many times each rule is matched in the markup.
Requires Node, can be installed with npm.
1. Start the extension scan
2. Scan all external CSS currently in use (page load)
3. Scan all inline CSS currently in use (page load)
4. Monitor (this is the missing piece of the puzzle): Developer uses the app and extension monitors new AJAX or JavaScript added CSS rules
5. Developer clicks a Finish and Report button:
a) Warning for inline CSS that could be moved externally
b) Warning for external CSS that is never used
c) Export (per CSS file, or combined and minified) CSS files, with unused CSS removed.