Imagine that i want to create a background image without set it into the html,body rules, but declaring it as a <div>
The problem is that this div will occupy the entire page and subsequent elements will go under it (out of page). So, it's would useful to make the background a "not-occupying" element, so that other elements can use his space.
There is a special rule in the css for do that? Hiding an element, it's possibile to set "display:none" rule, but is it possibile to do a similiar thing with the element regularly displayed?