2. Shared CSS across many pages
Multiple css files can work together across a site. This concept of multiple css files working together in a modular way is the heart of the cascade system of pages that all share code via links to master css files that control styles throughout the site. This system has obvious advantages: if all your pages share the same master css file, you can change the style of any component in the master css file, and every page of your site will show the new style. For example, if you tweak the typographic style of your headings in the master file, every heading throughout the site will change to reflect the new look.
In a complex site, page designers often link groups of css files to style a site. Packaging multiple css files can have many practical advantages. In a complex site css code can run to hundreds of lines, and it’s often more practical to subdivide such elements as the basic page layout css from the master site typography styles. It’s easy to link to css files and let the master css layout and typography styles control all the pages in your site.
CSS “skin” files for specific graphic treatments
You may not want every page or section of your site to look the same. If so, you can add a third “skin” css file that provides specific graphics, colors, and header treatments for all pages in a site section that share the same visual design. Each css file in the multifile cascade adds information, moving from sitewide general layout and typographic styles to visual styles that may be specific to a few pages (fig. 5.6).