It is very easy to do. It's not perfect, and there are missing pieces. But, it is really super easy once you understand the basics.

The problem isn't making one, it's making one that has enough complexity and configuration capability where you feel it's okay to give to other people.

Basically, you feel like it's simple enough that you can keep it to yourself and handcraft it as needed. Which is good, but also does raise the question "what is a theme?" indeed.