jc,
A great request and one we tried to tackle “quickly” a while back, but given all the valid constructs allowed in a CSS file, coupled with all the valid use-cases of CSS it became obvious very quickly that this was a big undertaking, and at the time we had much bigger fish to fry.
I’ll drop a line to the editor team and see if any changes in the more recent releases have made doing this any easier, because (for example) there is autocomplete for JSF style tags of CSS styles in some cases. So the support for something like this might be right around the corner.