body {
background-image: url(../images/background-blue.png);
background-repeat: repeat-x;
margin:0px;
padding:0px;
}
#container {
position:absolute;
left: 50%;
width:50em;
margin-left: -25em; /*set to a negative number 1/2 of your width*/
}
#header {
width: 247px;
height:59px;
margin-top: 35px;
margin-bottom: 36px;
margin-left: 35px;
margin-right: 518px;
}
#navigation {
width: 730px;
height: 50px;
margin-left: 35px;
margin-right: 35px;
margin-top: 0px;
margin-bottom: 0px;
background-color: #333391;
color: #ef8031;
font-weight: bold;
}
#navigation ul {
margin: 0;
padding: 0;
text-align: center;
display:inline;
list-style-type: none;
}
#navigation a{
display:block;
margin: 0;
padding: 0px;
height: 50px;
width: 150px;
color:#ef8031;
background: #333391;
text-decoration: none;
}
#navigation a:hover {
color: #fff;
background: #ef8031;
}
<!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>Home - MyMedia:Home Server</title>
<link href="css/main.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="container">
<div id="header"><img src="images/logo.png" width="247" height="59" alt="MyMedia Logo" /></div>
<div id="navigation">
<ul id="navigation">
<li><a href="#">Home</a></li>
<li><a href="#">Browse</a></li>
<li><a href="#">Search</a></li>
<li><a href="#">Add</a></li>
</ul>
</div>
</div>
</body>
</html>