There are many ways you can improve your CSS from combining selector, grouping and combining. But sometimes with large CSS files things can start getting out of control.
Using a web app will help you identify areas of your CSS your can improve on. These should be able to catch duplicate styles so you can group them therefore reducing the size of your CSS file.
Here is a list of websites you can use to improve your CSS file.
ProCSSor is a powerful (and wholly free) CSS prettifier that lets you format CSS in the exact way you want. It empowers you to turn your CSS into something that is visually more compelling, and with a minimum of effort at that.
CSS Lint is a tool to help point out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problematic patterns or signs of inefficiency. The rules are all pluggable, so you can easily write your own or omit ones you don't want.
You hate writing vendor prefixes for all browsers? Just let CSSPrefixer do it for you!
It's easy, fast and free.
You can now use powerful CSS3 techniques, and don't waste your time writing each properties.
First, write your code for your loved browser.
Then, come here, paste your CSS code in the first block, and prefix!
All vendor prefixes are added to your code. You can safely replace your old code.
CSS Drive CSS Compressor
Use this utility to compress your CSS to increase loading speed and save on bandwidth as well. You can choose from three levels of compression, depending on how legible you want the compressed CSS to be versus degree of compression. The "Normal" mode should work well in most cases, creating a good balance between the two.