Making a div fit the initial screen

Question

I want to make a div fit the initial height and width of a users screen.

I think the following crudely drawn diagram explain this better:

Answer 1

another way to do this with CSS only...

http://jsfiddle.net/pxfunc/qQ45K/

html, body {height:100%;} /* explicitly set html & body height */

#fillScreen {
    position:relative;
    top:0;
    left:0;
    height:100%;
    width:100%;
}