How to customize submit button on Drupal 8 contact form?

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function mytheme_form_contact_message_feedback_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) { $form['actions']['submit']['#prefix'] = ''; $form['actions']['submit']['#suffix'] = ''; $form['actions']['submit']['#value'] = 'Your value'; }

Sample blackbox block

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