Place ⅓ cup apple cider vinegar, 2 tablespoons olive oil, 2 tablespoons honey, 1 tablespoon whole grain mustard, ½ teaspoon celery salt, ¼ teaspoon kosher salt, and ¼ teaspoon black pepper in a large bowl and whisk until smooth.
Add ½ finely shredded medium green cabbage, 2 grated medium carrots, ½ thinly sliced small red onion, and 2 thinly sliced medium scallions to the bowl of dressing. Toss to combine.
