html, body {
  overflow: hidden;
  position: fixed;
}
body {
  margin: 0;
  padding: 0;
  background: grey;
  width: 100%;
  height: 100%;
  -webkit-user-select: none; /* Safari */        
  -moz-user-select: none; /* Firefox */
  -ms-user-select: none; /* IE10+/Edge */
  user-select: none; /* Standard */
}
#gc, #gcbg {
  display: block;
  margin: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  -webkit-user-select: none; /* Safari */        
  -moz-user-select: none; /* Firefox */
  -ms-user-select: none; /* IE10+/Edge */
  user-select: none; /* Standard */
  touch-action: none;
}
#gc2 {
  display: block;
  background: white;
}
canvas {
  image-rendering: optimizeSpeed;             /* Older versions of FF          */
  image-rendering: -moz-crisp-edges;          /* FF 6.0+                       */
  image-rendering: -webkit-optimize-contrast; /* Safari                        */
  image-rendering: -o-crisp-edges;            /* OS X & Windows Opera (12.02+) */
  image-rendering: pixelated;                 /* Awesome future-browsers       */
  -ms-interpolation-mode: nearest-neighbor;   /* IE                            */
}