I've already addressed frontend technologies like HTML and CSS in this series. In the backend you're free to use whatever technology you want to use, it only has to be available for the platform you're working on. And even that is no restriction, since you can also choose your complete server stack as you want. It does not affect the user. You can write your backend code in 68K Assembler and run it on such a chip, if you want. The only common characteristic the system has to have is to speak the IP / TCP / HTTP protocol stack to deliver the content to web clients. Therefore, there are many different backend technologies, some newer, some older, with different philosophies and communities of different sizes and compositions.
The frontend-part is completely different. The World Wide Web has ever been designed for a diverse set of client software (browsers), which means a specific website is not to be made for a specific browser (although that happens all day). And this results in a need for standards. Standards, defining in what form a web server can deliver content so that every of those clients will be able to render it. Such standards are HTML, CSS, JavaScript in their various versions and modules. While you're able to use whatever programming language, technology, web server software and such you want in the backend, you're eventually bound to write HTML documents the browsers can handle (well, actually there are some unpopular alternatives like XSLT, we've seen).
