To change the background of the header part, you need to use the HeaderBackgroundproperty. For the rounded corners, you will need to extract the default control template of the RadTabControl and make the respective changes to it.
From the screenshots, I am assuming that you are interested in the Crystal theme, so I've gone ahead and created a sample app with it for your convenience.
You can find the project attached to my reply. Please, give it a try and let me know if you found it helpful.
Best Regards,
Vicky
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