You can edit the backend theme of Sitefinity - the default one can be found in the SDK:
C:\Program Files (x86)\Telerik\Sitefinity 4.3\SDK\Content\Resources
Then you need to map it as any other theme in the settings section of the website ( please see attached ).
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items