Button on Focus underline the text

<zk>
    <style>
        .mybutton .z-button-focus .z-button-cm
            { text-decoration:underline;
            }
    </style>
    <window title="Button Focus!!" border="normal" width="600px">
        Press Tab to see the effect
        <button label="Button without Underline one Focus" onClick=""
            mold="trendy" />
        <button label="Button with Underline one Focus" onClick=""
            mold="trendy" sclass="mybutton" />
    </window>
</zk>