Be aware that the CSS for these layouts is heavily commented. If you do most of your work in Design view, have a peek at the code to g helloet tips on working with the CSS for the fixed layouts. You can remove these comments before you launch your site. To learn more about the techniques used in these CSS Layouts, read this article at Adobe's Developer Center -

Clearing Method

To remove the inline styles, make sure your CSS Styles panel is set to Current. Select the image, and in the Properties pane of the CSS Styles panel, right click and delete the display and background properties. (Of course, you can always go directly into the code and delete the inline styles from the image or placeholder there.)