only one column category and product after update

-- HikaShop version -- : 3.0.1 starter
-- Joomla version -- : 3.7
-- PHP version -- : 7

Although I found this topic in the forum hikashop one column Ican't find a solution for the same situation at my website. What do I miss?

Regards

EDIT: I found this in the css: .hikashop_subcategories div.hikashop_category, .hikashop_products_listing div.hikashop_product {
float: left;
width: 100%;
}
which I need to delete. It followed with the update I think because the same issue was here:
https://www.hikashop.com/forum/install-update/888412-only-one-product-column-after-update.html

Question: where can I find the frontend_custom.css file?

Regards

Last edit: I found the CSS and deleted the code. It's fine now. edit css