Additionally: in case you want to add containing div's to the submit button of the webform, here's a hook which will help you out:
function YOURTHEMENAME_form_alter(&$form, &$form_state, $form_id) {
if ($form['#form_id'] === 'webform_client_form_YOURWEBFORMID') {
$form_structure = &$form['submitted'];
$form['actions']['submit']['#prefix'] = '<div class="extra_div">';
$form['actions']['submit']['#suffix'] = '</div>';
}
}
If you want to apply this to all webforms, you just leave the conditional away, like this:
function YOURTHEMENAME_form_alter(&$form, &$form_state, $form_id) {
$form_structure = &$form['submitted'];
$form['actions']['submit']['#prefix'] = '<div class="extra_div">';
$form['actions']['submit']['#suffix'] = '</div>';
}