Hej husk alttid afslutte din html-head-body og andre ting
og du manglede et links til css
<!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">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="content-style-type" content="text/css" />
<link href="
http://1afghan.com/dewane.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="container">
<div id="header">
<h1></h1>
<ul id="mainmenu">
<li class="active"><a href="index.html"><span>Forsiden</span></a></li>
<li><a href="omos.html"><span>Om os</span></a></li>
<li><a href="kontakt.html"><span>Kontakt</span></a></li>
<li><a href="fordel.html"><span>Fordelsklubben</span></a></li>
<li><a href="aabning.html"><span>bningstider og priser</span></a></li>
</ul>
</div>
</body>
</html>