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

You can do this completely with CSS too:

html, body {
    margin: 0;
    padding: 0;
    min-height: 100%;
    width: 100%;
}

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