Issues are tracked in the CSS Working Group by the spec editors using one of the following mechanisms (per the editors' preference):
Each spec has a link in its header to where issues are tracked for the draft (e.g. see “Issues List:” in header of CSS3-UI editor's draft). If all issues are tracked in the draft itself, this points to the editor's draft.
If you have a better mechanism you'd like to use, please first propose it to the working group.
It is part of an editor's responsibility to bring issues to the WG for discussion when appropriate. This is not an escalating conflict-resolution mechanism. This is about the editor's job being to filter out and deal with obvious issue resolutions, and to coherently present the remaining issues to the WG for discussion and resolution.
(The CSSWG editor role is that of an intelligent secretary: you can freely draft things in the early stages, call the shots on the straightforward and obvious changes when you know the boss would agree and won't need to review personally—but you're not in charge here.)
The level of WG oversight on a spec depends on its maturity: the closer a spec is to REC, the less leeway the editor has for making unilateral decisions.
(This is actually good practice for all issues, not just Last Call. But it's especially important for Last Call.)
First, file the issue. Then, in your response include:
Good examples (better examples would link to the issue):
In some cases, the issue is more complicated and some back and forth is required. But at some point, there should be a final response that represents the editors' (or WG's) position, requests confirmation that it's acceptable, and gives the commenter enough information to make an informed decision about whether that position is acceptable.