#overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.85);
  overflow: auto;
  z-index: 9999;
  padding: 1rem;
}

#overlay-img {
  display: block;
  margin-left: auto;
  margin-right: auto;
  cursor: zoom-out;
}
img.zoomable {
  cursor: zoom-in;
}