Is the official w3c CSS spec and browser documentation, the ultimate Css reference? I dunno, seems logical, but is it the best way?
It is what most other documentation is based on, but is really aimed at browser developers and not to friendly for web developers.
There are lots of other good articles around the web that explain things much better.
A good listing of them is http://www.csscreator.com/links/linkspage.php
Hope that helps
Also consider a demo of Style Master (www.westciv.com) and TopStyle (www.bradsoft.com) - by the time the demo time is up, these programs have helped you learn a lot just by having the tag help and whatnot integrated.
I have the w3c html and css2 references saved and I refer to them now and again, but for practical tutorials (which is 99% of my time spent with CSS), nothing beats scouring the web for answers to real-world problems, I reckon.
I use the official w3c stuff more as a reference to look things up. Then I explore further by Googling.