Drupal 8 styling part of form field title

Question

i have form api element, in which i need to style only a part of it via a given tag

 $form['title'] = array(
  '#type' => 'textfield', 
  '#title' => '<p class="asterix para>"'.t('how much   quantity').'<span>'.t('...please specify').'</span></p>', 
  '#required' => TRUE,
);

the part in span tag, is differently styled. But the problem is, when i run drupal validation on this, the whole title along with tags comes in the message.