Adding id or class to native form

Lesson 1 – Overriding core fields: https://docs.woothemes.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/

You can add a class to the first example like so:
$fields['order']['order_comments']['class'] = array('my-class-name');

If you aren’t sure what code you need for your customization, you may want to look into hiring a developer:

– http://jobs.wordpress.net/
– https://codeable.io/