Thinly slice the cucumbers and red onion. If using regular cucumbers, you may want to remove the seeds first.
In a small bowl, whisk together the white vinegar, sugar, salt, and black pepper until the sugar is completely dissolved.
Place the sliced cucumbers and onions in a large mixing bowl.
Pour the vinegar mixture over the vegetables and toss gently to coat everything evenly.
Add the chopped fresh dill and toss once more to distribute.
Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to develop.
Before serving, give the salad a gentle stir to redistribute the marinade.
Taste and adjust seasoning with additional salt or pepper if needed.