Add class instead of hard coded width

The modal popup for notice.php has a hard coded width which is found here:

administrator/components/com_hikashop/helpers/cart.php

And looks like this:

echo '<div style="display:none;">'.
'<a rel="{handler: \'iframe\',size: {x: 675, y: 450}}" id="hikashop_notice_box_trigger_link" ref="'.hikashop_completeLink('checkout&task=notice'.$url_itemid,true).'"> </a>'.

This is not optimal for responsive design and mobile templates. How can we set a class instead for the width?

Thanks

Thanks