<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>CSS Masking: mask-position: position mask layer image</title>
    <link rel="author" title="Astley Chen" href="mailto:aschen@mozilla.com">
    <link rel="author" title="Mozilla" href="https://www.mozilla.org">
    <style type="text/css">
      div.outer {
        position: relative;
        width: 100px;
        height: 100px;
        border: 1px solid black;
      }

      div.inner {
        position: absolute;
        width: 50px;
    