HTML and CSS are not the answer. If anything, you should be scared off by the fact that webpages require at least three languages to implement anything useful (HTML, CSS, and JS), and that doesn't count whatever you could use for a backend (PHP? I'm not a web developer, so I don't know what the cool kids use, other than maybe Node.js.)
In my book, the fewer langauges you use, the better: I will even extend this to Qt and QML (and it should be pointed out that I am passionate about using Qt and QML!). Multiple languages necessitate (often fragile) bridges to work together; plus, they take much more time and effort to learn. If you could learn one language and use it to make an app, wouldn't you jump at that instead of learning 3 or 4 languages before you could make an app?
Others have already added some great comments about the wisdom (or rather the lack thereof) of integrating a web browser into the OS. Myself? I don't wish anybody a future of bloated webapps for everything.