Question
How can I theme a form element in drupal 8?
Solution
you can write your own form-element.html.twig or use preprocess_form_element() to add class in label or in wrapper element.
/**
* @param $variables
*/
function mytheme_preprocess_form_element(&$variables)
{
$variables['label']['#attributes']['class'][] = 'label-class';
$variables['attributes']['class'][] = 'wrapper-class';
}
