As of today, it seems the rendering enging of Gmail.com is broken. Simple CSS Styling from the <head> doesn't work anymore:

<html>
<head>
<meta charset="UTF-8">
<title>Naamloos document</title>

<style>
.background {
background:#000000;
}
td {
color:#ffffff;
}
</style>
</head>

<body>

<table width="100%" border="0" cellspacing="0" cellpadding="0" class="background" height="100">
<tbody>
<tr>
<td>Doesnt work</td>
</tr>
</tbody>
</table>
</body>
</html>

Any thoughts? 6 months ago something similar happened, it was indeed a bug where they did an update to the old render-engine from a few years ago.