Themes are used for changing the look and feel of an ATutor installation. Themes can be set as a personal preference or forced to display by default using the System Preferences Theme Specific Categories option.
ATutor's architecture allows for the separation of presentation elements from code or logic elements. As a result, it is easy for any XHTML and CSS proficient person to create customized themes and layouts without having to know anything about PHP or the inner workings of ATutor itself.