Changing the border for tr.shown

I'm sure this is a simple CSS fix, but I can't crack this.

I'd like a border across the top of the row with the child row, so I'm trying to modify the CSS of tr.shown to add it, but border-top never shows up.

Here's a demo:
http://live.datatables.net/joqezovo/1/edit

Am I not doing the CSS correctly? Is there something else I should be looking at?