What are your thoughts on this? I expect you might have hesitations about munging the user's CSS during load, however I don't know of any other way to accomplish this. 

It needs to be clear that `/user.css` should overrule all other rules. The whole point of it is for the user to change something specified in the theme. I was hoping that simply concatenating `/user.css` at the *end* of the theme css would be enough (ie, that later style declarations would overrule earlier ones) but that doesn't seem to be the case. And I tried it the other way around, and somehow that didn't work either. Somehow the CSS defined by the theme always wins in the case of a conflict.

So instead, I just mark *every* `/user.css` rule as `!important` and then it starts working like I expect.