Custom theme options for each element in responsive forms.
The ability to set custom styles and themes for specific items in the responsive forms.
For example.
I have added 2 buttons, I want one to show as blue and the other as red. This is currently not possible with the out of box theme designer.

Thanks for your suggestion Jake. We are currently building our new version of Responsive Forms and reconsidering how the style builder works.
We may reach out to you in the future for your feedback.
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Paul commented
Our users are requesting this now, too. Specifically, requesting dark mode or dark theme for Nintex Forms 365 (new responsive designer) in the browser. I tried to give them something myself, by inverting background and text colors, but it had several drawbacks. For instance, on our read-only text controls, it switched the font to gray (which I could not change) while the background was another shade of gray, which made it difficult to read.
I want to see an offering for an option that the user can check to flip back and forth to enable dark mode, and then give the designer more ability to customize those colors.