Change page width in simplex

Ok, sorry I was a little to hasty in my post. I figured it out or at least worked around it. I created another div with the attributes below to hold the entire page and and placed the tag below the body tag in header.php

background-color: #ffffff;
width: 900px;
margin-right: auto;
margin-left: auto;
border-left: 1px solid #999999;
border-right: 1px solid #999999;