How to adjust the CSS for CForms

Please don't change the CSS files directly (because of updates, prioritizing etc.). Insert the changes into your Joomla template CSS file (most times called template.css or custom.css).

We wrote a blog article on how to use Firebug to make changes on the CSS of an extension:

https://compojoom.com/blog/entry/how-to-use-firebug-to-change-the-css-of-a-joomla-extension