There's a "Coverage Support" experiment in Chrome DevTools which does css + js coverage in a way you describe it. The CSS part was shown on Chrome DevSummit 201

There's a "Coverage Support" experiment in Chrome DevTools which does css + js coverage in a way you describe it. The CSS part was shown on Chrome DevSummit 2016 [1] [1] https://www.youtube.com/watch?v=HF1luRD4Qmk https://www.youtube.com/watch?v=HF1luRD4Qmk