Adding rounded corners to sidebars

I've been working on chapter eight of CSS: The Missing Manual, in particular the section on creating rounded corners.

The book demonstrates how to round corners on fixed-width boxes, but there are a few links for boxes which are less than fixed.

They are: www.vertextwerks.com/tests/sidebars

www.sperling.com/examples/box

www.456bereastreet.com/lab/teaser/flexible

Once I've had a play around with the fixed-width boxes I will come back to them and hopefully give a proper run-down on them.