body {
    font: normal 20px Helvetica, Arial, sans-serif;

  }
<!--neue version...bald)
.text_navi{font-size:10px; color:#ccc;text-decoration:none;}
#impressum{margin-top:350px;}


-->

.hilfe_links{font-size:120px; font-weight: bold;}

  .loesung{font-weight: bold;}

  #hintergrund{
	z-index:1;
	background-color:#FFFFFF;
         position:absolute; top:50%; left:50%; width:600px; height:390px;
         margin-top:-180px;
         margin-left:-300px;
         }
    #hintergrund1{
	z-index:1;
	background-color:#FFFFFF;
         border:1px dashed black;
         position:absolute; top:50%; left:50%; width:600px; height:390px;
         margin-top:-180px;
         margin-left:-300px;
         }

 #headline_aufgabe{
         position:absolute; top:50%; left:50%;
          margin-top:-200px;
         margin-left:-300px;
         font-weight: bold;
         font-size: 12px;
          }


a.niveau span{display:none;}
a.niveau:hover span{
	display:inline;
	color:#FF0000;

         }
#text{
         position:absolute; top:50%; left:50%; width:220px;
         text-align:justify;
          margin-top:-160px;
         margin-left:40px;
         font-size: 12px;
         font-weight: bold;
          }
.text-light {font-size: 12px;
         font-weight: bold; font-weight: normal;}

#diagramm{
         position:absolute; top:50%; left:50%; width:220px;
         text-align:justify;
          margin-top:-170px;
         margin-left:-270px;
         font-weight: bold;
          }

 #zuruck{
         position:absolute; top:50%; left:50%;
         margin-top:-200px;
         margin-left:270px;
	}
 #zuruck a{
         text-decoration:none;
         color: black;
         font-size: 12px;
          font-weight: bold;
         }


  ul#Navigation {
    margin: 0; padding: 0;
  }

  ul#Navigation li {
    list-style: none;
    display: inline;
    margin: 0; padding: 0;
  }

  .green, .blue, .red, .black, .keine, .frage {
    float: left; width: 20px;
    margin: 0.0em; padding: 20px 20px;
    text-decoration: none; font-weight: bold;
  }

    .bild {
    float: left;
    margin: 0; padding: 6px 10px;}


  .green {background-color: #000000; color: white;}
  .blue {background-color: #000000; color: white;}
  .red {background-color: #000000; color: white;}
  .black {background-color: #CCC; color: white;}
  .keine {background-color: #ccc; color: #D2D2D2;}
  .frage {background-color: #ccc; color: #000000;}


  .green:hover {color: green; background-color: #000000;}
  .blue:hover {color: blue; background-color: #000000;}
  .red:hover {color: red; background-color: #000000;}
  .black:hover { color: #000000; background-color: #CCC;}


  ul#Navigation div {
     clear: left;
  }



#jahr2{position:absolute; top:50%; left:0px; margin-top:-180px; }
#jahr1{position:absolute; top:50%; left:0px; margin-top:-160px; }
#impressum{position:absolute; top:50%; left:0px; margin-top:-140px;
         }

.bt_archiv_text{

         display:none;
         }

.bt_archiv:hover span{
         display:block;
         padding-right:90px;
         padding-bottom:5px;
         font-weight: bold;
         color:#000000;
         background-color:#FFFFFF;
         background-image:url(bilder/archiv.jpg);
         margin-left:20px;
         margin-top:-30px;

         }

a.bt_archiv{


         background-color:#C253D9;
        /* background-color:#FF00FF; */
         color:white;
         padding-top:0px;
         padding-bottom:0px;
         padding-left:3px;
         padding-right:5px;
         text-decoration:none;
         font-size:10px;

         }
span.bt_archiv{



         color:black;
         padding-top:0px;
         padding-bottom:0px;
         padding-left:3px;
         padding-right:5px;
         text-decoration:none;
         font-size:10px;

         }

.bt_impressum{


         background-color:#C253D9;
        /* background-color:#FF00FF; */
         color:white;
         padding-top:0px;
         padding-bottom:0px;
         padding-left:3px;
         padding-right:5px;
         text-decoration:none;
         font-size:10px;

         }
a.bt_jahrgang{
        background-color:#C253D9;
        /* background-color:#FF00FF; */
         color:white;
         padding-top:0px;
         padding-bottom:0px;
         padding-left:3px;
         padding-right:5px;
         text-decoration:none;
         font-size:10px;

         }
span.bt_jahrgang{
         color:black;
         padding-top:0px;
         padding-bottom:0px;
         padding-left:3px;
         padding-right:5px;
         text-decoration:none;
         font-size:10px;

         }