Join Joe Marini for an in-depth discussion in this video What you should already know, part of Learning jQuery UI.
And finally, for CSS, James Williamson also has a course called CSS Fundamentals, which you should check out if you need help with CSS. jQuery UI is also built on top of the popular jQuery library, so you might want to have some passing familiarity with jQuery syntax and how it works. If you want to brush up on your jQuery, I have a course here on Lynda.com called jQuery Essential Training. Once you feel that you've got the basics down and you're prepared to move on, we can begin with the course.