#gallery {
  position: relative;
  padding-top: 50%;
  -moz-user-select: none; user-select: none;
}

#gallery img {
  position: absolute;
  top: 25%;
  left: 12.5%;
  max-width: 24.5%;
  max-height: 49.5%;
  -webkit-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
  -moz-user-select: none; user-select: none;
  cursor: zoom-in;
}
#gallery img:nth-child(4n-2) {left: 37.5%;}
#gallery img:nth-child(4n-1) {left: 62.5%;}
#gallery img:nth-child(4n) {left: 87.5%;}
#gallery img:nth-child(n+5) {top: 75%;}

#gallery img:focus {
  position: fixed;
  top: 50%;
  left: 50%;
  z-index: 31;
  max-width: 100%;
  max-height: 100%;
  outline: none;
  pointer-events: none;
}

#gallery img:focus ~ div {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 30;
  background: rgba(240,240,240,.9);
  cursor: zoom-out;
}