Design Options can be used to set the Content Area's height (fixed height or stretch) and to set the position of the site (top or center).
When the Content Area Height is left blank the site will stretch vertically as content is added to the page. It is recommended to set the Site Position and Entrance Content Position to 'top' if the Content Area Height is left blank. That way the page header will always be in the same (top) position when displaying a shorter page with little content.
If the Content Area Height is set to a number (a fixed height), it is recommended to set the Site Position to 'center'. That way on a higher resolution screen, the site will appear in the center rather than at the top with a lot of blank space below it.
If the Entrance Page contains only a little content it is also recommended to set the Entrance Content Position to 'center'.