function buttonOn(img) {
  img.src = "./img/img/left_menu/on__"+img.id+".png";
}
function buttonOff(img) {
  img.src = "./img/img/left_menu/off_"+img.id+".png";
}
function showHide(id) {
  element = document.getElementById(id);
  if(element.className=="schovat")
    element.className = "";
  else
    element.className = "schovat";
}