function change_bg_color(bg_color) {

  document.getElementById('counter_preview').bgColor=bg_color;

 }

 function delete_query(confirm_txt) {

  if(confirm( confirm_txt )) {

   return true;

  }
  else {

   return false;

  }

 }



 var Marker = "true";

 function CheckboxenAktivieren() {

  if(Marker == "false") {

   for(i = 0; i < (document.getElementById("button_form").length)-2; i++) {

    document.getElementById(i).checked = true;

   }

   Marker = "true";
   return "Auswahl aufheben";

  }
  else {

   for(i = 0; i < (document.getElementById("button_form").length)-2; i++) {

    document.getElementById(i).checked = false;

   }

   Marker = "false";
   return "Alle makieren";

  }

 }