[IMP] e-commerce onboarding misc improvements [bst]

Task: https://www.odoo.com/web#id=10453&view_type=form&model=project.task&action=327
Pad: https://pad.odoo.com/p/r.eQNwZOFNkcYt31Sw
override the button font for specified readable theme. but only those button whose haven't <code>.fa-shopping-cart</code> class.