Problem/Motivation
It's important for administrative elements to maintain consistent elements and a visual language even if they are being presented to the user alongside the front-end of the site. For example the Toolbar and Edit modules.
Currently this is very difficult or impossible to do, the CSS loaded by the front-end theme affects the admin elements and theme functions are also passed through the front-end them. This produces an amazing amount of inconsistency depending on the theme and commonly breaks admin UIs that are display on the front-end.
The Overlay module worked around this by loading the admin UI inside of an iframe.