It would be really helpful if you can share your experiences.....
I understand that when I embed Marketo form in external non-Marketo LP, the form would be responsive if the LP is so.
However, there is an exception, which is rich text area created in the form. It isn't still non-responseve. I myself can't come up with the way of changing it responsive but I guess it is a common issue so please let me know your best solution.
This question would get a lot more visibility in our Products and Support, can you please move it there by clicking 'move' on the ride side of your post? This Champion area is to learn about and discuss the Champion program where as Products & Support is the area to ask product related questions and manage your support experience.