I wrote that for my company ~3 jobs ago, except instead of working only on static HTML, it would: for a small percentage of our traffic loop in the background p

I wrote that for my company ~3 jobs ago, except instead of working only on static HTML, it would: for a small percentage of our traffic loop in the background processing a couple CSS selectors at a time, adding CSS selectors that matched to a bloom filter that would be occasionally POSTed back to the server. Then I'd parse through our logs, pulling out the bloom filters, and comparing them to our CSS rules to find unused rules. It wasn't perfect so it required manually checking before deleting CSS rules but it went a long way towards flagging potentially unused CSS rules.