@media only screen and (-webkit-min-device-pixel-ratio: 2), only screen and (min-device-pixel-ratio: 2) {
   .replace-2x {
      font-size: 1px;
   }
   .example {
      background-image: url(../images/example2x.png);
      -webkit-background-size:13px 13px;
      -moz-background-size:13px 13px;
      -o-background-size:13px 13px;
      background-size:13px 13px;
   }
}