CoffeeBox pairs dark chocolate with coffee through familiar roasted, nutty and caramel-like associations. That is a useful starting idea, but a high cocoa percentage and a deep roast do not guarantee harmony. Bitterness can reinforce bitterness, and a brighter coffee can provide an enjoyable contrast instead of an automatic clash.
Taste the coffee and chocolate separately first. Note sweetness, bitterness, acidity and texture, then try a small piece of chocolate followed by a comfortable sip. Compare the aftertaste rather than expecting one ingredient to chemically cancel the other. Use modest portions and keep the coffee preparation constant if comparing several chocolates.
A milk chocolate, a fruitier dark chocolate and a very intense dark bar can lead to different preferences even with the same coffee. Read ingredients where dairy, nuts or other allergens matter. Processing and origin labels can suggest a direction but do not dictate the pairing. The point is to find a combination that keeps both enjoyable, rather than follow a fixed cocoa-percentage rule or assume that a flavor wheel provides one correct match for every palate.
The conversation
A good question can make a better brew.