<!DOCTYPE html>
<title>CSS Reference: mask-image</title>
<link rel="author" title="Xidorn Quan" href="https://www.upsuper.org">
<link rel="author" title="Mozilla" href="https://www.mozilla.org">
<style>
#ref {
  position: absolute;
  width: 200px;
  height: 200px;
  background: green;
}
</style>
<p>The test passes if there is a green square and no red below.</p>
<div id="ref"></div>