CSS doesn't load background pictures for <header>

Question

Right now I'm working on an HTML5+CSS3 homework. I'd want to have a dynamic header image. So ot was awesom 'till the pont when I made it "dynamic".

Currently: There isn't any kind of header in my page. Plase help. :) Here the CSS:

header{
position:static;
margin: 0 auto;
background:url(img/desk_header.png);
background-repeat: no-repeat;}

Here is the HTML:

<header></header>

Answer 1

Setting width and height might help

header{
  position:static;
  margin: 0 auto;
  width: 100%;
  height: 50px;
  background:url(img/desk_header.png);
  background-repeat: no-repeat;
}