Add to cart button overrided

-- url of the page with the problem -- : www.aquanano.ro
-- HikaShop version -- : 3.4.0
-- Joomla version -- : 3.8.7
-- PHP version -- : 5.6
-- Browser(s) name and version -- : all
-- Error-message(debug-mod must be tuned on) -- : No error, just problem

I can't get to use the add_to_cart button. I mean, the .png picture, with the shopping basket on it. In fact, whatever the style would be, I can use only the simple button for add to cart, no matter what I tried, as I have some override wich I can't find (as I am almost a noob in coding) . For now, I let the settings in place for using one of the template's button (btn class I think), but still, I would like to find the override for displaying a nicer button, as I have for another website, https://coloidale.ro/index.php/ro/produse/argint-coloidal-si-ionic . Still, in https://aquanano.ro/index.php/category/18-argint-coloidal-si-ionic-aquanano , "I" couldn't do it, and believe me, I spent some hours looking...

Any help would be appreciated.

Paul