body
{
  background-color: black;
}
.Zentriert
{
  position: absolute;
  margin: auto;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  width: 900px;
  height: 450px;
  background-color: black;

}



<!--  

  border-radius: 20px;




-->