To apply styles to more than a single Web page at a time, create an external style sheet and either link it to each Web page or have the browser import it into each page. As of the time these materials were created, importing did not work reliably in either major browser, thus linking is recommended.
The idea is that if you create a separate document with the style definitions, you can refer each Web page to the sheet of defined styles and an entire Web site is styled with just one sheet of styles. Naturally, changes to any of the styles would affect the entire site automatically and immediately.
To create an external style sheet:
The name of the external style sheet will appear in the Edit Styles or <style> dialog box. If created while the Web page was open, the link for the current page is automatically created. Other pages will need to be linked separately (see four lines below).
To define styles on an external style sheet:
To link additional pages to an external style sheet:
Any of the styles in an external style sheet can be edited and the changes immediately apply to every page that uses that style sheet.
To edit an external style sheet:
The beauty of external stylesheets is not only that you need only create the styles for all pages once, but that if you change the style definition, all pages using those styles automatically change without even opening the pages that are linked to the external stylesheet. Thus, effects like seasonal color changes are easy to apply to every page in a Web site.