This project is not under active development anymore.
There are better ways to customize windows on modern macOS (using full size content view or customizing the titlebar view).
NSWindow subclass with support to custom titlebar height, background color and title color
You can contribute with code, just send me a pull request, or open an issue for any bug/enhancement.
Disclaimer: sending a pull request does not mean I will accept It, if I don't accept your pull request It doesn't mean I don't love you ;)
If you like this and will use It to make your app look funny, you can show me some love by donating through PayPal