100% Css-layout with header and footer

[See it in action]

  #header { 
    position:absolute; 
    height: 50px; 
    left:0; 
    top:0; 
    width:100%; 
    background:green;
  }

  #footer { 
    position:absolute; 
    height: 50px; 
    left:0; 
    bottom:0; 
    width:100%;
    background:green;
  }

  #content { 
    position: absolute; 
    top:50px; 
    bottom:50px; 
    left:0;
    width:100%;
    background:#eee; 
  }

  #box1 { 
    height:50%; 
    width:30%; 
    float:left; 
    background:red; 
  }