Its impossible to master every subject. If you know how to code and know you should just know your way around all these technologies , that might actually be obsolete before you manage to master them.
You should not be a CCS3 guru. You should know how everything works, but when you do not use it for some time you will forget syntax, what does what..., but when you should work on it, its just a matter of few days to get things rolling again (and few or alot google searches)
If you build 4-5 BIG projects you will surely know your way around stuff
Certainly you have to keep an eye on knew trends and web standards (i.e offline applications, notifications etc etc).
If you need to learn something its not that hard if you know your stuff. For example if you want to use SASS , just read or watch some videos for few days and you are ready to go. Its not rocket science. Just syntax.