#bg {
  /*position: fixed; */
  top: 0; 
  left: 0; 
	
  /* Preserve aspet ratio */
  min-width: 100%;
  min-height: 100%;
}

#zentriert {
  margin: auto;
  border: 3px solid #73AD21;
  margin-left: auto;
  margin-right: auto;
  position:middle;
}