Laravel - Embed Form in another website using a script (example)

Hello wonderful community of IH :)

I found this script which is being sold on Codecanyon: https://socialproofo.com/demo/

They have a very interesting feature which is something I have been researching before stumbling upon this script.

They have a line of code (they call it a pixel) which can be placed on the end-users website and the code will inject the software being used by the user from the main application, from the end-users account in the application.

I was originally looking at iframes as I want to allow users to embed a form from my laravel application onto their own website (the users create their own forms in my software).

Does anyone understand what is going on here, or have an explanation of how this works? I just cannot fathom how UI, CSS, HTML and JS is being pulled from an online Saas application and being injected into a site all with one line of code? Genius I say!

Also would this sort of thing be achievable using a form in Laravel or am I correct continuing on the path of iframe?

I hope this is all ok and clear enough to understand, any questions I'd be more than happy to elaborate :)

Kindest Regards