html, body {
 margin: 0;
 padding: 0;
 height: 100%;
}
#headerInner {
 margin: 0 auto;
 position: relative;
 width:990px;
 min-width: 990px;
}
#hauptmenue {
 background-image: url('../images/back_mnu_aktivitaet.jpg');
}
#content {
 height: 1200px;
 min-height: 1200px;
}