CSS
Edit
- In the Performance panel, Enable "advanced rendering instrumentation (slow)" in Settings.
- Click Record, and perform the operation on the page that affects rendering.
- In the recorded profile, identify a long style recalculation and select it in the waterfall view (“Main” section).
- In the bottom tab bar, click Selector Stats. Sort the selectors based on Elapsed Time, Match Attempts etc., to identify expensive selectors.