A dead comment asked if stealing 100 dollars if fine if you give it back.

So I'll chip in that for basic theft, one of the core elements is intent to permanently deprive the original owner. So if someone steals money, changes their mind, and then returns it, that's still theft. And taking money to spend, with a promise of returning money later, still counts as theft. But if the intent all along was to return it the next day, stored safely the entire time, that's not theft.

Obviously intent is hard to prove, so don't try to pull that off without a lot of evidence and/or a very understanding target.