Introduction

It's a good idea to use the minified 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"
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Click on "Run Test"
You will see a well-detailed result of web page performance test
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Click on "Tools"
You'll see all available tools
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Click on YUI CSS Compressor, it'll open a new tab and you will get the minified CSS
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