Is there anything specific that you want to learn, or just basics? If so, you can start with http://www.w3schools.com Good luck!
For beginners, I'd suggest w3schools.com or tizag.com, after you've learned all that, the best way to learn more is from experience, just try and make some websites and projects using css, you'll learn more as you go.
Yes, w3school.com is the best. You can also visit the link in my signature. It has many tutorials about programming and web design. Check it out.
It also might be a good idea to pick up a book on CSS from your local library if you don't have the time or resources to try and become familiar with CSS by experience.
The way I learned CSS was with the lynda videos. Go to lynda.com and search for CSS. You probably won't find a better more thorough set of tutorials.