As we know, Drupal does not seperate the frond-end and back-end totally, so the theme of front-end and back-end is the same, though you can set the Administrator theme in admin/settings/admin/theme, there is still some situation that will make you crazy, you can see my another article about it. [Drupal] Use administrative theme when deleting or reviewing the content node
Lucky, some person has built a wonderful module to handle with that situation.
This module: Administration theme , is very helpful to do that.
you should read more of it because it provide wildcard of url to do what you want.