In a large bowl, whisk together the vinegar, oil, syrup, mustard, garlic, celery salt, and pepper. Set up your food processor with the slicing blade. Drop Brussels sprouts down the chute to finely slice them. Alternatively, use a sharp knife and carefully slice the Brussels sprouts. Transfer them to the bowl with the dressing. Remove the slicing blade from the processor and set up the grater attachment. Push carrots through the chute to shred. Alternatively, use a box grater to shred carrots. Transfer the shredded carrots to the bowl. Add the scallions and toss everything together. Garnish with almond slivers and serve immediately or chill for 30 minutes before serving.