Tweak of template design for primary links menu (willing to pay for that)

Hello,
I would like to have primary links design like that on the screen shot. Just need to create 2 half rounded backgrounds for the top right and white background for links below (When link is active or highlighted). I think that can be done easily in css but I don't have idea how....
If you can help me with that, I can pay a few $ for your time.
Regards

Charlie