01 - Combine the green cabbage, red cabbage, carrot, and green onions in a large bowl.
02 - Whisk together the mayonnaise, apple cider vinegar, Dijon mustard, sugar, celery seed, salt, and pepper in a separate small bowl until smooth.
03 - Pour the dressing over the vegetables and toss until everything is evenly coated.
04 - Taste and adjust seasoning if needed.
05 - Cover and refrigerate for at least 30 minutes before serving to allow flavors to meld.