Need to edit CSS on MarketPress

I can't seem to get the css right for my marketpress store.. you guys help me and it looks great.. then there's a problem on different size devices and a difference between single product view and grid view

the buy now button and the price need to be aligned under the the product image for grids - and depending on device it's not... then on the individual product pages, it's not aligned on full screen, but is on mobile.

Support Access enabled.