Hi Neff,
I was able to find a great example where you can see the code and an explanation on how to accomplish what you are looking for here . In the example they use the Wix Window API and the Wix Stores API .
If you do not want to use Corvid, you can add a standalone add to cart button and assign a product to it. The button will trigger a light box. For information on how to do this, click here.
Best regards,
Edward | Corvid Team