<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
span { display:block; outline: 10px solid yellow; }
</style>
</head>
<body>
<div>
<div style="display: -moz-inline-grid">
<span>M</span>
<span>N</span>
</div>
</body>
</html>