@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;
  }
}