Hi eliot,
Thank you for reply.
I did some digging in the files and found this file: <joomla>\components\com_hikashop\views\checkout\tmpl\address_view.php. This has a modal class applied to an a tag with this ID: id="hikashop_checkout_<?php echo $this->type;?>_address_edit_<?php echo $address->address_id; ?>" and has a class: "modal hikashop_checkout_<?php echo $this->type;?>_address_edit". I copied it to: <templatename>\html\com_hikashop\checkout and have changed it to: "btn hikashop_checkout_<?php echo $this->type;?>_address_edit".
The change is seen in the attached image.
I am ok with this look. Do you think changing this class will affect any the look elsewhere?