If you work with stylesheets you will often find redundant selectors in your document. If you set about identifying them manually, it would take a lot of time and effort. Gladly, there is a web application that does this for you within seconds.
CSS Redundancy checker identifies the unused elements of your stylesheet. Simple specify the URL of your stylesheet and the URL of your HTML pages. The application will then search your stylesheet and find selectors that are not being used anywhere in those HTML pages. It is a very useful tool to clean a stylesheet.
It is also a good tool to identify which selectors are being used on which HTML pages. However, for that purpose you will have to try one HTML page at a time.