From the beginning I want to mention that, at least to me, the title of this goal sounded a bit too ambitious. Which doesn’t mean that one cannot Master CSS...

It’s just the feeling that, in web design & development, no matter how much you know, given the crazy pace at which everything is evolving and changing, you never seem to quite attain the master status :)
But then, even the masters need to learn and improve themselves ;) So even if I feel that I still have quite a lot to learn, I feel like I have attained this goal.

And, yes, it is worth all the effort! Because XHTML + CSS are the present and the future of web design.