Joomla takes a big leap into the mobile space with a total overhaul of both its frontend design and administrator interface. With the adoption of the Bootstrap framework, Joomla! has become the first major CMS to be mobile ready in both the visitors and administrator areas.
Bootstrap is integrated into the Joomla User Interface (JUI) library. This allows Joomla developers to easily create standardized backend & frontend interface for their extensions.
When you install the latest ACL Manager version in Joomla 3.0 the interface is using this new JUI library, following the standardized backend interface of Joomla 3.0. You can check out some screenshots below. The interface of ACL Manager installed in Joomla 2.5 is not using Bootstrap, so still the same.