If you use Firefox and any of these IDEs: (IntelliJ IDEA, RubyMine, PhpStorm, WebStorm, PyCharm), you can use CSS-X-Fire [1] to do precisely that (edit in browser, (optionally) reflect changes in IDE). Nevertheless it's a very good achievement for a JS-based app!

[1] http://code.google.com/p/css-x-fire