Of course, a single style won't transform a web page into a work of art. It may make your paragraphs red, but to infuse your websites with great design, you need many different styles. A collection of CSS styles comprises a style sheet. A style sheet can be one of two types—internal or external, depending on whether the style information is located in the web page itself or in a separate file linked to the web page.
Most of the time, external style sheets are the way to go, since they make building web pages easier and updating websites faster. An external style sheet collects all your style information in a single file that you then link to a web page with just a single line of code. You can attach the same external style sheet to every page in your website, providing a unified design. It also makes a complete site makeover as easy as editing a single text file.
On the receiving end, external style sheets help web pages load faster. When you use an external style sheet, your web pages can contain only basic HTML—no byte-hogging HTML tables or <font> tags and no internal CSS style code. Furthermore, when a web browser downloads an external style sheet, it stores the file on your visitor's computer (in a behind-the-scenes folder called a cache) for quick access. When your visitor hops to other pages on the site that use the same external style sheet, there's no need for the browser to download the style sheet again. The browser simply downloads the requested HTML file and pulls the external style sheet from its cache—a significant savings in download time.
When you're working on your website and previewing it in a browser, the cache can work against you. See the box on Internal Style Sheets for a workaround.