Here's an example of the problem. I created a blue rectangle and stretched it across the width of the screen. However, when I preview the site, the blue rectangle is centered in the middle with white space on both ends. Back in design mode, I tried stretching the rectangle off of the page on both ends, but it still recenters in the middle when I preview. This also happens to a placed image. How do I get elements to fill the width of the browser window?