sbClick = function() {
  var cont = document.getElementById("select_bezirk");
  cont.onclick = function(){
    var select = document.getElementById("list_bezirk");
    switch(select.style.display){
       case "block": 
         select.style.display = "none"; 
         break;
       default: select.style.display = "block"; 
    }
  };
}

sbClick();