The best way to analyze your CSS is to use the CSS analyzer, but if you're in a hurry or if you want an opinionated tool, then you can use this CSS Code Quality analyzer. It will use the output of the CSS analyzer to run a couple of checks and turn that into a set of recommendations for your CSS. It will focus on Performance, Maintainability and Complexity and score each one of them between 0 and 100 points. Think of it like PageSpeed Insights, but for CSS.