如何将“选择选项”更改为Fastcart下拉列表

When using Big Commerce, is there a way to change the "Choose Option" button when your item has multiple sizes? See below, the button on the right is one item with one size, while the button on the left is one item with multiple sizes.

The goal is to provide the user with one-click add to cart functionality, similar to what the "Add to Cart" button does (also know as: "Fast Cart")

I was hoping that there was a way to edit the Snippets/CategoryProductsItem.html page to allow this to happen, but I am new to the platform.

I've found the theme file which outputs the view on the website:

 <div class="ProductActionAdd" style="display:%%GLOBAL_HideActionAdd%%;">
        <a href="%%GLOBAL_ProductURL%%" class="btn Small icon-%%GLOBAL_ProductAddText%%" title="%%GLOBAL_ProductAddText%%">%%GLOBAL_ProductAddText%%</a>
    </div>

I know that the $_GLOBAL signifies a variable, but what can I do to change the logic of the theme, which will display a drop down and show all the sizes for the product?

Thank you for your help.