I haven't seen a tool doing a break down yet.<p>You can find unused CSS with <a href="https://github.com/giakki/uncss" rel="nofollow">https://github.com/giakki/uncss</a> and linters, e.g. <a href="https://github.com/brigade/scss-lint/" rel="nofollow">https://github.com/brigade/scss-lint/</a>, will analyze and warn if the complexity (number of levels etc) grows too big.