Use of CSS Standards

The use of CSS improves the interoperability of web resources by allowing authors to separate the styling of content for different media (i.e. graphical screen, printer, etc.) from the content itself. This allows the author to use the same source content for rendering on a wide range of technologies or create special stylesheets to control the rendering on particular devices.

CSS Specifications

W3C CSS Validation Service

The W3C CSS Validation Service can be used to validate the CSS associated with HTML/XHTML documents.

CSS Web Resources

CSS Books