#Kontakt {
  background-image: url(overlay.png);
  position: absolute;
  margin: auto;
  top:  0;
  left: 0;
  z-index: 100;
  width:  100%;
}

* html #Kontakt {
  background-image: none;
} 

#m_window3 {
  position: absolute;
  background: #fff;
  border: 5px solid #fff;
  overflow: auto;
  width: 400px;
  height: 455px;
  z-index: 150;
}


#m_frame3 {
  border: 0; 
  overflow: auto;
  width: 100%;
  height: 455px;
}