Also, here are some articles I found in my links list:
CSS Stress Tester Bookmarklet (Copy into a bookmarklet. Then it will tell you the rules that are causing the most lag.)
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Old but still relevant I think: http://www.stevesouders.com/blog/2009/06/18/simplifying-css-... Text makes CSS slow (don't render too much): https://news.ycombinator.com/item?id=2232212 In general, following good guidelines might help: https://github.com/csswizardry/CSS-Guidelines