function scroll_up(div){
  var element = document.getElementById(div);
  var top = parseInt(element.style.top);
  top = top + 200;
  if (top >= 0){
    top = 0;
  }
  element.style.top = top + "px";
}

function scroll_down(div,height){
  var element = document.getElementById(div);
  var top = parseInt(element.style.top);
  top = top - 200;
  actualHeight = element.offsetHeight;
  scrollHeight = (height - 150) - actualHeight;
  if (top <= scrollHeight){
    top = scrollHeight;
  }
  element.style.top = top + "px";
}