new grid system in MarketPress 2.8

I’ve been working on trying to get a three-across grid system using the previous version of MarketPress and now I see that you have created exactly what I need in the new version. Problem is that after updating to 2.8 my products in the list view appear one under the other rather than three across the page. I wonder whether this is due to modifications I have made to the styling conflicting with the new 2.8 CSS. Any clues? See