function navigate()
  {
   document.getElementById("navigace").style.position = 'absolute';      
   zhora = document.body.scrollTop;
   if(zhora<265) zhora = 265; else zhora = zhora+5;
   document.getElementById("navigace").style.top  = zhora; 
   zleva = ((document.body.clientWidth-840)/2)+50;
   if(zleva<50) zleva = 50;
   document.getElementById("navigace").style.left = zleva;                
   setTimeout("navigate()", 10);
  }