Is there a way to check which CSS styles are being used or not used on a web page?

Google Chrome has a two ways to check for unused CSS.

1. Audit Tab: > Right Click + Inspect Element on the page, find the "Audit" tab, and run the audit, making sure "Web Page Performance" is checked.

Lists all unused CSS tags - see image below.

Update: - - - - - - - - - - - - - - OR - - - - - - - - - - - - - -

2. Coverage Tab: > Right Click + Inspect Element on the page, find the three dots on the far right (circled in image) and open Console Drawer (or hit Esc), finally click the three dots left side in the drawer (circled in image) to open Coverage tool.

Chrome launched a tool to see unused CSS and JS - Chrome 59 Update Allows you to start and stop a recording (red square in image) to allow better coverage of a user experience on the page.

Shows all used and unused CSS/JS in the files - see image below.

Install the CSS Usage add-on for Firebug and run it on that page. It will tell you which styles are being used and not used by that page.

Just for completeness and because it was asked in the comments - there's also the CSS audit tool in Chrome now for the same purpose. Some details here:

http://meeech.amihod.com/very-useful-find-unused-css-rules-with-google