A key consideration when working with SharePoint CSS is in how SharePoint references CSS files. By default, SharePoint master pages use a SharePoint control named
<SharePoint:CssLink> to retrieve uncustomized CSS files, including corev4.css, from the Web front-end server. In addition, when you create custom CSS files, you also reference those files in the
<head> section of the site’s master page using relative links. When you add links to a master page to reference CSS files, you are referencing external CSS files—either on the Web front-end server or in the site collection’s Style Library.
However, SharePoint also uses internal and inline CSS in Wiki pages, page layouts, and master pages. For example, the v4.master ...