How to add class to all forms automatically? I want to add .form class to all Drupal forms.  How can I add class to all forms by overriding theme function?
You can do something like this:

function MYMODULE_OR_THEME_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  $form['#attributes']['class'][] = 'MY_CLASS';
}