body { margin: 0; padding: 0; width:100%; height:100%;}
 
#container_zeichenflaeche
  {
  position: absolute;
  top: 50%;
  left: 50% ;
  background: #ffffff;
  width: 800px;
  height: 600px;
  color: #000000;
  border: 0px solid black;
  padding: 0px;
  z-index: 2;
  margin-left: -400px;
  margin-top: -300px;
  }

  #container_button
  {
    position:absolute; 
    top: 90%; 
    left: 60%;   
  }