<html>
<head>
<style>
div {
  display: -moz-box;
  display: -webkit-box;
  display: box;
  width: 100px;
  height: 100px;
}

div.outer {
  background-color:red;
}

div.inner {
  background-color:green;
  -moz-box-flex: 1;
  -webkit-box-flex: 1;
  box-flex: 1;
  width:10px;
  height:100px;
  display: block;
}
</style>
</head>
<body>
<p>You should see a single 100x100 green square below. If you see any red, then
the test has failed.</p>
<div class="outer">
<div class="inner"></div>
</div>
</body>