function showForm (id) {
  var elem = document.getElementById(id).style.visibility;

  if ( elem == 'hidden' ) {
    document.getElementById(id).style.visibility = "visible";
    document.getElementById(id).style.position = "static";
    document.getElementById(id).style.display = "block";
  } else {
    document.getElementById(id).style.visibility = "hidden";
    document.getElementById(id).style.position = "absolute";
    document.getElementById(id).style.display = "none";
  }
}