no response for button style

-- HikaShop version -- : 3.1
-- Joomla version -- : 3.7.0
-- PHP version -- : 5.5.38

hi

i am trying out hikashop 3.1 before upgrading. i would like to use BS buttons but i dont know if i should choose normal or css.

i tried switching settings but this class still appears

<a rel="nofollow" class="hikashop_cart_button" href="#" onclick="var field=document.getElementById('hikashop_product_quantity_field_1');if(hikashopCheckChangeForm('item','hikashop_product_form')){ return hikashopModifyQuantity('34',field,1,'hikashop_product_form','cart'); } else { return false; }">Add to cart</a>

i already replaced it with btn btn-success.

still nothing.

what am i missing. thanks