How does codeigniter allow for friendly urls?

[eluser]Unknown[/eluser]
Thank you all for your responses, but I think I didn't explain myself clearly. I am not working under CI. I am working on a personal project inspired by CI. One of the things I admire from CI is its ability to use friendly urls. I've figured out how to parse the URI and load the appropiate controller, but when this happens the browser thinks I'm calling the CSS in a directory relative to the URI. At "www.example.com/index.php", the default controller is called and the css is also called correctly at "www.example.com/resources/style/default.css". However, at "www.example.com/index.php/blog/", the controller "blog" is found and loaded, but the css is called incorrectly at "www.example.com/index.php/blog/resources/style/default.css". I am trying to make it so when I make any HREF, it does it from the base url of the website, not from the URI (or URL? Not entirely sure here.) Again, thanks for your responses!