This bit highlighted in red gets rid of the problem ... for now. I'm not sure why making .product-box inline-block is doing that.
border: 2px solid #C9C9C9;
box-shadow: 0 0 13px #808080;
Any reason for using the paragraph tag so much? I see you use empty p tags for creating space around your heading, you also wrap anchors, images and div elemtents with p tags. If you look at it semantically, those are not paragraphs and the p tag should not be used there.