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:

#div
{
 width: 100%;
 height: 100%;
}

does not seem to work

Answer 1

If I understand correctly (there’s some room for confusion here):

http://jsfiddle.net/zRpNp/

#screenFiller {
    position: absolute;
    top: 0; right: 0; bottom: 0; left: 0;
    border: 15px solid orange
}

You might be after the position: fixed version: http://jsfiddle.net/zRpNp/1/