function showByClass(selectClass) {
  var allTags = document.getElementsByTagName("div");
  for (i=0;i<allTags.length; i++) {
    if (allTags[i].className == selectClass) {
        allTags[i].style.display = 'block';
      }
    }
  }
function hideByClass(selectClassOff) {
  var allTags = document.getElementsByTagName("div");
  for (i=0;i<allTags.length; i++) {
    if (allTags[i].className == selectClassOff) {
        allTags[i].style.display = 'none';
      }
    }
  }