A cascading style sheet provides a great, flexible way for controlling the look or presentation of your Web pages. Small changes to this one document can dramatically change the appearance of many Web pages. This easy method for controlling the design of your pages allows you to rapidly implement changes to the look and feel of your Web site. The CSS elements are often called style rules, and can be inserted directly in a Web page or separately in an external file. There are three different methods in which CSS styles can inserted in a Web page: inline style, embedded or internal style, and external style.

Whereas HTML is a semantic language, Cascading Style Sheet (or CSS) is a presentational language.  It is the perfect complement language to HTML and it was designed primarily to work with HTML.  CSS is more a language of rules than a normal programming language such as Visual Basic, Java, or C#.  In other words, you will not find a loop statement or a function call in CSS.  The style rules and standards are set and maintained by the World Wide Web Consortium (W3C).  In a nutshell, CSS is a simple language that defines style constructs to format the appearance of a Web page.  The style rules define a set of formatting instructions (one or more property-value pairs), that affect the HTML elements in a Web page.

CSS has several versions or levels.  Each newer version is built on top of the previous version.  CSS1 was introduced in 1996 followed by CSS2 in 1998 and CSS3 in 2005.  At the time this was written, CSS3 was still the most up-to-date version used in today’s web development.  Even though CSS3 was released more than a decade ago, many new properties and rules were gradually introduced.  This chapter covers many of the standard CSS properties and rules and some of the new CSS3 properties.

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