After a quick look it appears to be a conflict with your theme CSS. Your theme uses the same CSS expressions as the store does and so one is overriding the other. They both use a form of 960_24_col.css. You either have to edit your theme/page templates (and the corresponding theme stylesheet) with different names or try a different theme. You could try changing all the store CSS tags, but there are far too numerous and it would take you a very long time.
The main culprit (to start with) is container_24 which appears in both the store CSS and the theme CSS: /themes/u-design/styles/common-css/960.css