em.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en">

<head>
<title>test</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css">
div {
	font: 12pt normal sans serif;
}
div {
	margin: 0;
	padding: 0;
}
#twenty_em {
	width: 20em;
	border: 1px solid #000000;
}
#ten_em {
	width: 10em;
	border: 1px solid #000000;
}
</style>
</head>

<body>
<div id="twenty_em">mmmmmmmmmmmmmmmmmmmm</div>
<div id="ten_em">mmmmmmmmmm</div>
</body>

</html>