ecommerce product page using vanilla HTML, CSS and JS

HELP! I gave up on the lightbox view cause the only solution I could think of would be to rewrite the whole html, css and javascript when it is exactly the same as components that I already made on the site. I am sure there is a better way to solve the issue using the code I have already made. So if anyone could review my code and give me an easy solution that would be great! Or if I would have to write my code differently from start so it would be easier to implement the lightbox view. Thanks!