<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>CSS Masking: mask-image: mask with opacity</title>
    <link rel="author" title="CJ Ku" href="mailto:cku@mozilla.com">
    <link rel="author" title="Mozilla" href="https://www.mozilla.org">
    <style type="text/css">
      div {
        position: absolute;
        left: 10px;
        top: 60px;
        background-color: rgba(0,0,255,0.5);
        width: 100px;
        height: 50px;
      }
    </style>
  </head>
  <body>
    <div></div>
