function angebot() {
  document.getElementById('angebot').style.visibility='visible';
  document.getElementById('angebot_bg').style.visibility='visible';
  if (window.innerWidth){
  document.getElementById('angebot_bg').style.width=window.innerWidth;
  document.getElementById('angebot_bg').style.height=window.innerHeight;
  }
  else {
  document.getElementById('angebot_bg').style.width=document.body.offsetWidth;
  document.getElementById('angebot_bg').style.height=document.body.offsetHeight;
  }
}

function close_angebot() {
  document.getElementById('angebot').style.visibility='hidden';
  document.getElementById('angebot_bg').style.visibility='hidden';
}