The obvious solution is to block the server-side pages that the CSS elements link to. This kind of tracking can be mitigated the same way any other kind of tracking is already handled by uBlock or uMatrix.
Example: You visit example-site.com
example-site.com is the php server that sends you the html. It also the site that does the tracking. So when you click something it sends that data to example-site.com and then it can forward the data to a third-party tracking service.
If you blocked or used host files on the server-side pages then the site example-site.com would be completely blocked too.
Ultimately if everyone uses ad-blocks to block tracking script they can be added to the back end. If you block the back-end you effectively block the website you are accessing in the first place.