Why aren't my borders showing up?

Hi! I’m working on this page (I know the URL looks weird. That’s another problem I’m trying to fix with my hosting service): http://74.220.215.230/~guntools/redi-bore-caliber-chart/

There is a table on the page but the horizontal borders are not showing up. I changed the table background colors to white instead of grey. But for some reason I can’t find the CSS code for the horizontal borders. I’m using theme iDream.

Does anyone know what I need to edit to make these lines show up?