CSS

This docuent demonstrates how to apply fixed margins to the columns of a flexible layout without adding extra markup or anticipating what elements may be used inside the columns.

<style media="all" title="stylesheet" type="text/css">
    body { margin: 0; padding: 0; }
    #content { float: left; width: 80%; background-color: #ccc; }
    #content * { margin: 1em 20px; }
    #content * * { margin: auto; }
    #sidebar { float: right; width: 20%; background-color: #ddd; }
    #sidebar * { margin: 1em 20px; }
    #sidebar * * { margin: auto; }
</style>

HTML

<div id="content">
    <p>CONTENT</p>
</div>
<div id="sidebar">
    <p>SIDEBAR</p>
</div>