Question

I want to fill the screen (width and height) on any size with a <header>:

<header></header>
    <div id="content"></div>
<footer></footer>

The <header> should always fill the whole screen on any height of monitor also in iPad, such that the content of <div id="content"> will only be seen after scrolling, not before that.

Answer 1

Simply give your html, body & header a height of 100%:

html, body, header {
    height: 100%
}

http://jsfiddle.net/tujsj/