Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation semantics (the look and formatting) of a document written in HTML and XHTML.
There are several ways to add CSS to an HTML page
1. External CSS File Include
2. Internal Style Sheets Include
3. Inline Style Include
5. Applying CSS Styles using JQuery
check the following link for more details and example
For more CSS Info CLICK HERE