If you have tested some css code, and when we delete some code, there may be some css code are not used, if we want to delete these code to decrease the size of a page, it will spend more time. There are some css check tools can help us to check if the css code is unused.
1. Dust-Me Selectors
Dust-Me is a powerful Firefox Plugin, it can spider your page like a google robots, then check all the css file and css style the page have used, and find the unused css code.When you open your page or your local file in Firefox, click the right button of your mouse,
Note: This plugin can’t spider the css that between <style> and </style> that in your current page.
2. Google Page Speed
If you are using Google Webmaster Tool, you may be reminded to add Page Speed. This Plugin is based for Firefox famous Plugin Firebug. You will never regret to use google page speed, it can not just check your css, it also help you to optimize your page, and increase the speed of your page by check your image, your js and so on.
Learn More: https://developers.google.com/speed/pagespeed/