A set of additional tags that describe the appearance of individual HTML tags. The style sheet tags describe the font, color, paragraph alignment, and other attributes for common HTML tags such as headings, paragraphs, and lists. These tags can exist within your document or as a separate text file.
When the style sheet is included with a Web page, all the tags on the Web page that have corresponding entries in the style sheet are automatically formatted according to the style sheet description. If the set of tags exists as a separate text file, it can be applied to one or more HTML documents.
Cascading style sheet (CSS) information is ignored by browsers that do not support this feature.
For more information, see Site Consistency.