Style properties that or added or deleted aren't outdated, in the same way that new templates or deleted templates aren't outdated (and therefore aren't flagged as such).
In the case of new and deleted templates, XenForo is very good at documenting these when there is a new update. Add-on developers should do the same (and some do, though admittedly some do not) for both new and deleted templates as well as new and deleted style properties.