function ShowUpozornenie() {
	/* Obtain reference for the selected boxID layer and its button */
	var element1 = document.getElementById("upozornenie");
	var element2 = document.getElementById("header");
	
	/* If the selected box is currently invisible, show it */
	if(element1.style.display == "none" || element1.style.display=="") {
		element1.style.display = "block";
		element2.style.display = "none";
	}
	/* otherwise hide it */
	else {
		element1.style.display = "none";
		element2.style.display = "block";
	}
}

<!-- script na bublinu okolo buttonu Facebooku - BEGIN -->

function visibilityON(element){

  var e=document.getElementById(element);

  if(!e)return true;

  e.style.display="block"

  return true;
}

function visibilityOFF(element){

  var e=document.getElementById(element);

  if(!e)return true;

  e.style.display="none"

  return true;
}

<!-- script na bublinu okolo buttonu Facebooku - END -->