That's not how web frameworks work. There is code on the server side which _generates_ the HTML, CSS and sometimes Javascript as well. So viewing the source in your browser can give you some clues, but this doesn't reveal what is going on on the server.
Just look at the source of the landing page. A lot of JavaScript and the usual kinds of structure that modern pages have.
> Where's its source code(Is it open sourced)?
Just right-click the page in your browser and view source.