First of all thanks for your tool it is so powerful and well thought that a child can use it ;)
Do you plan to manage the shorthand properties at some point? I am working on a huge application that have thousands of css rules (not the best part of the application code ;)) and most of them are in a short syntax.
I loved your tool to be able to handle that properly and not me to check backgrounds. As I am working with teams and I don't want them to be forced to use a syntax (We are already doing so much in house stuff that box us).
Otherwise we will write a tool or improve yours (Which will take longer that to you).