<!DOCTYPE html>
<title>Reference: mask-image: url(data:...)</title>
<link rel="author" title="Mats Palmgren" href="mailto:mats@mozilla.com">
<style>
#back {
  position: absolute;
  box-sizing: border-box;
  width: 200px;
  height: 200px;
  border: 60px solid green;
  background: blue;
}
#front {
  position: absolute;
  box-sizing: border-box;
  width: 200px;
  height: 200px;
  border: 40px solid blue;
  background: green;
  mask-image: url(1x1-black-30-alpha.png); /* 1x1 black with 30% transparency */
}
</style>
<p>The test passes if there is a blue-ish square with a 20px green border around it and a 40px blue-green-ish border around that.</p>
<div id="back"></div><div id="front"></div>
