External style sheet

An external style sheet is simply a text file containing CSS rules and saved with a file extension of .css. This file is then linked into all web pages that want to implement the styles defined within the external style sheet through the use of the HTML <link> tag. This is a commonly used method for splitting out the styling from the main web page and gives you the ability to change the look of an entire website through the use of a single external style sheet.

These are the basic concepts that you need to understand with regard to CSS. You can use CSS to define styles for pretty much anything on a web page including backgrounds, text, fonts, links, lists, images, tables, maps, and any other visible objects.