Trying to create web version of app for personal portfolio

Have question in relation to a side project I'm looking to start for my portfolio. I would like to create a web version of the myus shopping app.

One of the main questions is how does it contain these well known sites within the app? I have tried iframes in my site but often these sites don't allow iframes so wondering how they are within myus app?

Second question is the add to cart functionality, I am at a loss as to how it has its own add to cart when browsing on app.

Link to app image: https://images.app.goo.gl/1BHr9yF8Kw3kp6VS9

Many thanks in advance

28064212

The app is basically a browser - they can run whatever javascript they want to add bits to the site they're rendering. It's nothing to do with iframes.

Also, they have a browser extension, so what you're looking at basically already exists: https://chrome.google.com/webstore/detail/myus-shopping/jdohdiappiakacbmckagohongolonbpj

Oh yeah fully understand it slready exist but just want to try recreate for my own learning development