Aside from recent developments like NodeJS, the lack of interest in JavaScript as a server-side language is really weird. Both Microsoft and Netscape had JavaScript server scripting back in the 1990s, but people instead glommed onto ad-hoc languages written from scratch (PHP) or plucked others out of complete obscurity (Ruby) and made them successful.

I can't help to think that history would have been completely different if someone had created an Apache mod_js 10 years ago.

JavaScript is all we have on the client side, but on the server you can choose the best tool for the job. Languages like Ruby and Python are basically supersets of the semantics of JavaScript, but with many more features and large standard libraries. And these languages evolve, while JavaScript have been basically frozen for a decade. The server side language have well-tested libraries for working with the file system, databases and so on.

JavaScript is a nice, minimal language, but a bunch of other languages are just better when you are not constrained by the browser.

Besides, the benefit of having the same language on client and server might not be so great. Sure it looks nicer, but the programming model on client and server is quite different anyway.

Node.js is interesting. I suspect the users will soon want some syntactic sugar for dealing with asynchronicity (something like the new "await" keyword in C#). This is also neede on the client side, but much harder to get support for. But if they extend JS on the server side, does it make sense to compile down to vanilla JS rather that just forking the language?

Actually, you don't even need CSS, all you need is HTML. So it comes down to two (any server-side language, basically, plus HTML), one of which is not even a programming language.