The actual "magic" is happening somewhere in backend, right?

Nope, all of it happening directly in the frontend as this is a fully non custodial real lightning node. The only "back end" is just a dumb networking proxy server so you can connect peer to another node on the network. As more nodes like CLN start to accept websockets, this won't be needed at all.

Oh but the other "back end" is just an esplora based chain source. Right now In the near future, allowing users to select their own.