These Out Of Box (oob) CSS Styles are defined and stored in, and subsequently pulled from, the database.

To update or change these style definitions, you should create a new CSS Style using the "!important" tag that will be applied using the same name as the existing style included on your page. This will allow for the new style to override the existing oob style, and as well only update it on the page that it is included on. This is more preferred because it only affects this one page, and is the more correct way to do this.

More information about the "!important" tag can be found on the
World Wide Web Consortium (W3C) site, using the following URL: http://www.w3.org/TR/CSS2/cascade.html#important-rules