add/change div wrapper around specific radio button?
If you're defining the form yourself you can wrap an element with HTML using the #prefix and #suffix properties:

$form['radios'] = array(
  '#type' =&gt; 'radios',
  '#title' =&gt; 'Options',
  '#options' =&gt; drupal_map_assoc(1, 2, 3),
  '#prefix' =&gt; '&lt;div class="some-class"&gt;',
  '#suffix' =&gt; '&lt;/div&gt;'
);


If you want to add a class to the existing wrapper you can do so using the #attributes property:

$form['radios'] = array(
  '#type' =&gt; 'radios',
  '#title' =&gt; 'Options',
  '#options' =&gt; drupal_map_assoc(1, 2, 3),
  '#attributes' =&gt; array(
    'class' =&gt; array('some-class')
  )
);


If you're not defining the form yourself then you can still use the same logic and implement a hook_form_alter() to change the existing form:

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'some_form_id') {
    $form['some_element']['#attributes']['class'][] = 'some-class';
  }
}


Note that when using the hook_form_alter() method you should append to the existing classes array so as not to override any classes that have been set previously.