How to learn reinforcement learning

Greetings. I am an older guy who has programmed for 40+ years and wants to learn more about reinforcement learning and maybe code a simple game like checkers using reinforcement learning.

I want to understand the math being reinforcement learning better. It's been a couple decades since I've gone through the calculus path, but I am confident that with some work I could learn. And, I'd prefer to do something hands on where I do some coding to demonstrate I actually understand what I'm learning.

I've looked at a few tutorials online and they all seem to use some RL libraries, which I'm assuming are just going to encapsulate and hide the actual math from me, or they are high level discussions of the math.

Where can I find an online or book form of a discussion of the theory and mathematics or machine learning with an applied exercise in the programming world?