<!DOCTYPE html>
<html>
    <head>
        <title>Spanner between rows, margins</title>
    </head>
    <body>
        <p>There should be a blue square below.</p>
        <div style="margin:20px;">
            <div style="width:10em; height:2em;"></div>
            <div style="width:6em; height:3em; background:blue;"></div>
            <div style="width:6em; height:3em; background:blue;"></div>
        </div>
    </body>
</html>