We used this at my last company. We backported decisions into them as documentation. People sometimes referred to them, but not often. It was hard to take what was a huge list of docs, some of which had been obviated by others, and truly grok them all. But I don’t have a better idea for how to solve the problem. I would say it worked OK, but not great.
If you don’t do a ton of CSS but think you have a handle on it…this survey will dispell you of that notion :) Never felt more dumb in my life than answer “never heard of it” to most of the questions about different CSS features.