Someone asked me where they could learn CSS. The following have easy to understand, well-organized online tutorials.
W3Schools.com - http://www.w3schools.com/css/default.asp
EchoEcho.com - http://www.echoecho.com/css.htm

You have no doubt noticed that a lot of redesign is going on across Web sites, with softer colors and different fonts. Maybe it is a reflection of the aging baby-boomer generation that dark (usually black) type on a white background seems to predominate (easier to see). Or, maybe it is a reflection of more awareness of Section 508 of the U.S. Rehabilitation Acts Amendment of 1998. If you use CSS and have coded your pages properly, making small changes across several or hundreds of pages is the same. For example, you change the font in your CSS stylesheet and every Web page linked to your stylesheet will use this new font as soon as it is reloaded in someone’s browser (assuming it is not reloaded from their locally cached version).

By using CSS, you can more easily design Web pages for different browser audiances. You can test the kind of browser with JavaScript, PHP, or some other Web programming language, and select the style sheet that is appropriate. For example, someone who is browsing on a cell-phone is not going to want to view all of your images, and they may need different font sizes or colors. A common use of two different stylesheets is one for normal viewing and one that has been modified for printing.

The following Web sites are my favorite for more advanced CSS Web design.
A List Apart, CSS articles and tutorials http://www.alistapart.com/topics/css/
css Zen Garden: The Beauty in CSS Design http://www.csszengarden.com/
Eric Meyer: CSS http://www.meyerweb.com/eric/css/
Eric Meyer: CSS/Edge http://www.meyerweb.com/eric/css/edge/
Glish.com CSS layout techniques http://glish.com/css/

You should always validate your CSS. Though it is more convenient and faster if you buy an HTML/XML/CSS editor, which can validate your code —such as BBedit on the Macintosh— you can also check CSS online through the W3C validation service: The W3C CSS Validation Service,

My favorite book for getting started is the Visual QuickStart series book HTML for the World Wide Web by Elizabeth Castro (0321130073). CSS is covered sufficiently for the beginner and it will have you using CSS within minutes. Like all of the VQS books, it is a very handy quick reference guide.

My other favorite CSS books are
The Zen of CSS Design : Visual Enlightenment for the Web (Voices That Matter) by Dave Shea and Molly E. Holzschlag (0321303474).
Eric Meyer on CSS: Mastering the Language of Web Design by Eric A. Meyer (073571245X).

The International Webmaster’s Association - HTML Writer’s Guild (IWA-HWG) http://hwg.org periodically offers both beginning and advanced CSS courses.

For the library tie-in to this posting, see the Creative Librarian blog entry Library Webpage Examples which critiques the design of a number of library Web sites. Note that these Web sites may have changed since her weblog entry in January 2004. Laura Blalock includes a link to NYPL: Style Guide.

Futher Research
See U.S. Access Board for section 508 A Federal Agency Committed to Accessible Design for People with Disabilities
Usability.gov - U.S. Department of Health and Human Services - Usability: Accessibility Resources