How to make comments have zebra stripe

Hi

I am using a subtheme of the bootstrap theme. I want my comments to have a zebra stripe effect and am having trouble.

I am guessing this is easy as I see the $zebra variable in the comments tpl.php file. And in bootstrap Less I see where the color is selected for table background accent, which works when you choose the table-striped class for a table.

But somehow there is something missing either in my LESS file or the comment.tpl.php file, and my comments do not exhibit any striping.

Any pointers would be very helpful.