<!doctype html>
<style>
#target {
  width: 200px;
  height: 200px;
  background-color: green;
  /* blocked because the URL's port number doesn't match this document's origin. */
  -webkit-mask-image: url("http://localhost:8080/resources/square100.png");
  -webkit-mask-repeat: no-repeat;
  -webkit-mask-position: center;
}
</style>
<div id="target"></div>