Its all really done using css!

CSS styles

#wait_animated_icon {
  border: 6px solid #f3f3f3;
  border-radius: 50%;
  border-top: 6px solid #00ff00;
  width: 50px;
  height: 50px;
  -webkit-animation: animated_icon_spin 2s linear infinite; /* Safari */
  animation: animated_icon_spin 2s linear infinite;
  
  margin-top: 10px;
  margin-left: auto;
  margin-right: auto;
  margin-bottom: 10px;
  visibility: hidden;  /*Include this so element will only be shown when DisablePageUntilReloaded() is called*/
}

/* Safari */
@-webkit-keyframes animated_icon_spin {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(360deg); }
}

@keyframes animated_icon_spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

To show it using javascript

wait_animated_icon.style.visibility = "visible";