Altering the shape of the wrap border

[Maz]

My website is: http://arashmazinani.com

I have seen this blog http://katiekellerphotography.com/blog/ and I've noticed the top of what looks like the wrap border is curved and the on the bottom of the blog there are lots of little bumps.

I'm wanting to 'round off' the corners of the wrap border on my blog how does one go about doing it?

I'd imagine I'd have to readjust my header shape to compensate for it or is it a clever trick where the wrap border stops and it is actually the header that is rounded?

Although that would not explain the bottom of the blog?

Can anyone shed any light on this?

Thank you