What a underrated tool and work! It is a real great helper.
I have installed it at OBS 31.0.3 at my Mac Studio M2 and it runs perfect. You must only change the path to file:/// and uncheck "local file" as in other posts described. Boom. I only miss a short description "How to create own CSS styles". Yes, it has something to do with the style-source.css - but it is much difficult than expected :-)
The connection between an OBS dock and an interactive browser source, the option to manipulate content via dock directly, is fascinated and should be more in focus. Great tool and - again - it works still in 2025. And at a Mac too.