2em; height: 6em; margin-top:0}
    .ref { background-color: #009900; width: 12em; height: 6em; margin-bottom: 0}
    .test {background-color: color(srgb 0% 60% 0%)}
</style>
<body>
    <p>Test passes if you see a green square, and no red.</p>
    <p class="ref"> </p>
    <p class="test"> </p>
</body>