body { height:100%; }
#navi{
  position:absolute; left:0px; top:0px;
  width:20%; min-height:99%;
  background-color: #88ffff;
}
#inhalt{
  position:absolute; left:20%; top:0px;
  width:79.5%; min-height:99%; z-index:-1;
  background-color:#ffcccc;
}