Well, if you owe money al pi din and don’t pay it, you are stealing.
However, the civil law may affect what the din torah is as well. For example, I’d wonder if personal bankruptcy would be recognized by the torah, since when you lend money it is essentially al tnai that I can go bankrupt and not pay you back.
Once we go that far, we might wonder whether everything we do is essentially al tnai like that. Like if you buy a car, you might imagine it is al tnai that there is a Lemon Law. Or that if you sell shares in a public company, it is al tnai you won’t break the SEC rules.
Hmmm.