Is there an element called background...

Height: 100% works perfectly in standards mode. Use XHTML 1.1 or similar, but use
html, body { height: 100%; } to make the containers have a height of the minimum the viewport. Then you can use your div. However, both body and html support backgrounds, so place backgrounds in them first. Also, you don't need to give z-index to elements if because children will have higher z-indicies automatically.

There are also numerous javascript frameworks that give you drop-shadow, rounded corners or whatever you'd like to use multiple backgrounds with. Also, CSS3 supports multiple backgrounds in its current draft.