.overlay {
  overflow: hidden;
}

#toc {
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.5s, visibility 0s 0.5s;
  position: fixed;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  background: rgb(255,255,255);
  z-index: 5000;
  overflow-x: hidden;
  overflow-y: scroll;
  -webkit-overflow-scrolling: touch;
}

#toc iframe {
  height: 100%;
}

.overlay #toc {
  opacity : 1;
  visibility: visible;
  transition: opacity 0.5s;
}