Can anyone explain this?

This is a simple test. Can you explain why this border is not showing up?

TIA

http://www.gruenebydesign.com/csstest.html

invalid CSS.
border-[left|right|top|bottom] is a shorthand that should contain width style and color.
You may also want to consider using one element in place of four.

Ahhh, I see. Silly mistake.

Thank you