<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>CSS Masking: mask-origin: mask positioning area</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 {
        border: 1px solid black;
        width: 100px;
        height: 100px;
        position: relative;
      }

      div.inner {
        width: 50px;
        height: 50px;
        background-color: purple;
        position: absolute;
      }

      #border { left: 4px; top: 1px; }
      #padding { left: 10px; top: 9px; }
      #content { left: 13px; top: 15px; }
    </style>
  </head>
  <body>
    <div class="outer"><div class="inner" id="border"></div></div>
    <div class="outer"><div class="inner" id="border"></div></div>
    <div class="outer"><div class="inner" id="padding"></div></div>
    <div class="outer"><div class="inner" id="content"></div></div>
  </body>
</html>
