What is CSS?
CSS -- Cascading Style Sheets -- is a text-based system used to specify formats. CSS information is included or linked to by the pages on the website, and the author can then use simple tags to apply those formats to portions of the web page. These override the default settings: for instance, if a CSS style sheet specifies that level 1 headings (<H1> tags) are to appear in green, then they will appear in green rather than the standard black. CSS styles can work at any one of three levels -- page level, site level or web level -- and they can contain two types of settings, tag redefinitions and new classes.
Page level (embedded) CSS -- this requires the style sheet code to be embedded in a web page -- usually in the <HEAD> tag section at the top. The code then applies to that page only. To apply the same styles to another page the entire <STYLE> block must be copied and pasted into the new page.
Site level CSS -- somewhere in the website a single page is stored, usually with the extension .CSS, containing style definitions. Each page on the website is then linked to that page via a tag in the <HEAD> tag section, like this: <LINK REL=StyleSheet HREF="style.css">. When the user downloads the web page the link is activated and the styles are applied to the page as it appears on the screen.
Web level CSS -- an extension of the former in which the web page is stored somewhere else on the Web and the link includes a complete URL: for instance <LINK REL=StyleSheet HREF="http://www.acmeco.com/masters/style.css"> This remote style sheet can thus be applied to hundreds or thousands of pages around the world. If a change is made to the remote sheet it immediately affects the formatting of all the pages that are linked to it.