To integrate with your theme, you need to find the CSS selector of your button and paste to Corner Ribbon Add to Cart → Advanced → Selectors → Enter your selector. Then it'll be possible to update the add to cart button of your theme.
First, you need to go to a product page → add to cart button will appear.
Right click on the add to cart button → Inspect.
The developer tool will appear and auto detect the HTML tags of your button (usually starting with <button>).
Right click on the <button> (or what highlighted) → Copy → Copy selector.
You've successfully copied the CSS selector of your button.
Go to Corner Ribbon Add to Cart → Advanced → Selectors → Enter your selector → paste to CSS Selector of your button.
Done! You've successfully integrate with your theme.