add class to form element
You might be looking for the #attributes property that you can add to forms and form elements. See example below

function ajax_register_form_user_login_alter(&amp;$form, &amp;$form_state, $form_id) {
   $form['fbuser'] = array(
      '#type' =&gt; 'item',
      '#markup' =&gt; 'You have a facebook account?',
      '#weight' =&gt; -10,
      '#attributes' =&gt; array('class' =&gt; array('my-class-1')),
    );
   $form['login_link'] = array(
      '#type' =&gt; 'item',
      '#markup' =&gt; '&lt;a class="facebook-action-connect" rel="nofollow" href="foo"&gt;&lt;img src="foo" alt=""&gt;&lt;/a&gt;&lt;/div&gt;',
      '#weight' =&gt; -6,
      '#attributes' =&gt; array('class' =&gt; array('my-class-2')),
    );
   }