<!DOCTYPE html>
<html>
    <head>
        <title>Block that becomes spanner</title>
    </head>
    <body>
        <p>Below there should be a blue box, then a yellow box, then a blue box again.</p>
        <div style="-webkit-columns:2; columns:2; -webkit-column-gap:0; column-gap:0; orphans:1; widows:1; line-height:2em; background:blue;">
            <div style="-webkit-column-span:all; column-span:all; margin:4em 0; background:yellow;"><br><br></div>
        </div>
    </body>
</html>