Round corners in widgets

I can't figure out how to make round corners in the widget container.
I manage to make in the page/center column, but the same code don't work if I put it in the widget container.

You can see the page here: http://www.freelancekonsulenten.dk/
I would like to have the white area in the widget with round corners like in the page.

Any body who can help?

Thank you.