Customize CSS product listing with DIV boxes

How and where I can customize the CSS or maybe the whole HTML-Code für the menu "option=com_hikashop&view=product&layout=listing" ?
In the option parameters I selected box with rounded corners.
Thats OK, but on my page I have youst boxes with rounded corners, and I like to have them the same style.
I tried to make changes in the CSS file
media\com_hikashop\css\frontend_default.css
but without any effect on that page. Where this styles for the div boxes comes from?
Thank you

Rolandus

You need to edit the hikashop options of your product listing menu and you will see a rounded corner option there.
You can edit these options by editing your menu via the menu Display->Content menus.
The one in the configuration is only for when you create new menus.

OK, thats what I did already.
But what I want to know is:
- where I can find the CSS-Files included in this option to define the box and the rounded corner
- where I can find the PHP File, where is defined the HTML Code for the product listing?

Thank you

Since these are options, the CSS is added dynamically in PHP to the header of the HTML page. So there is no CSS file for that. It's added via PHP in the file administrator/components/com_hikashop/helper/module.php

The product listing id displayed by the files of the product view in the folder components/com_hikashop/views/product/tmpl