body {
 background-color: #000;
 }

#unten {
 background: url(logo.png);
 position:fixed;
 height: 466px;
 width: 700px;
 margin-right: 5px;
 margin-left: -350px;
 z-index:0;
 top: 300px;
 left: 50%;
}
#oben {
 background: url(logo_text.png);
 position:fixed;
 top:40px;
 left:50%;
 margin-left: -350px;
 width:700px;
 height:200px;
 z-index:1;
}