Would require embedding a full CSS parser in the Java side of the application. Not impossible, but not a high priority.
You could make a 'stub' style class (with no actual effects) so that it shows up in the selector, and then do all of the actual CSS authoring in the stylesheet. The big downside there is maintenance burden. I'm personally in favor of the idea of allowing arbitrary CSS editing inside a style class (with a one-way operation to convert the builder into a plain text input), but I also don't make any decisions re: Perspective 