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.