Sekmeyi sola/sağa yaslayınca(sekme boyutunu yarıya indirince) background yatay hizada tekrarlamıyor.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<style type="text/css">
body{
margin:0;
padding:0;
}
div#header{
background:repeat-x url('http://i42.tinypic.com/2wm1f6q.jpg');
width:100%;
height:75px;
border-bottom:1px solid gray;
}
div#header div#content{
width:1000px;
height:75px;
margin:0 auto;
}
</style>
</head>
<body>
<div id="header">
<div id="content">
<!-- İçerik -->
</div>
</div>
</body>
</html>