Hi,
Do you understand that every stylesheet in the CSS folder for your template gets picked up and is "in play"? There are 3 stylesheets in classic/css ... stylesheet_new and stylesheet_original plus the print stylesheet. The first 2 are controlling how your site is being styled and displayed.
You didn't style the class assigned to the table that makes up the "site" in stylesheet_new (the class assigned by Zen is "centershop"), but it is styled in stylesheet_old... it's set at 750 px. So you need to change that to either a fixed width or 100% or simply remove the width at all and let the table expand to fill available space.
Plus I believe that the order in which they are linked in affects the styling used -- a later stylesheet in the load order overrides an earlier one (just like an inline style overrides a linked stylesheet). I'm not sure how ZenCart determines the linking order since I don't use multiple stylesheets in this manner.
Does that make sense?
HTH,
Becky



