I'm also super interested in this thread. I tried looking everywhere for this info and just can't get it to work.
I'm editing an email collection item and just can't seem to get anything working. No matter where I insert the customised CSS, whether it's in the custom embed code, in my own page CSS or in the .cashmusic.org page, nothing works.
It did, briefly and then, when tried to reproduce the success on my page, it went back to the dark theme without changes.
I would love to use your tools, they seem to be exactly what my band needs.
Maybe a short tutorial on how to edit simple CSS attributes for those buttons? I literally just need to edit the sign up button colour in the light theme.