Javascript to alter styling of components on a page

I've built a site using a basic page builder (this one: spreadsimple.com), but need the UI to be slightly different.

I need the product cards (see an example here: https://oculus-amazon.spread.name/) to have different styling, and ideally additional functionality. However, I can't edit the html/css - I can only add in scripts (to "head", before "/body", and after "body").

I'm looking for somebody to write scripts to alter the styling of the cards on the page.