It's a good idea to use the minfied version of CSS (Cascading Style Sheets).
It'll minimize the page load and thus result in performance grow up.
What do you need?
Installation order : Mozilla Firefox > Firebug > YSlow
When you will have completed installation. Open a website and press "F12"
Click on "Run Test"
You will see a well detailed result of web page performance test
Click on "Tools"
You'll see all available tools
Click on YUI CSS Compressor, it'll open a new tab and you will get the minified