Add content block in cart page

Site URL: https://blenny-whale-rexw.squarespace.com/config/

I am trying to add a content block in the cart page. The content I am hoping to show are just one particular category of products (anniversary, birthday cards). 

The intension is to allow the customers to add cards to the cart after they have added a product to purchase from the website. 

Squarespace doesn't allow us to add pop ups. I think we can add JavaScript , but how to create that section while square space wouldn't let us edit the cart page content directly. 

I was wondering if we can add a section in the cart page before they checkout. 

Thanks in advance

You can add it into Footer, then we can give the code to move it to Cart Page

Hey, 

Thanks for that tip. 

Will I be able to cross sell/ upsell with this option ? 

Please let me know if you have the code. 

Cheers

You want this? Lightbox Plugin.