-
SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
Of course it’s not all butterflies and rainbows, you’ve already touched on the css limitations such as the positioning fixed & the likely difficulties you’ll face if implementing a drag to upload feature, but if you can live without these features, and for some such a the lack of media queries, you can easily work around by calculating width with Dimensions or this library https://github.com/kasinskas/react-native-media-query#readme (not used this myself so not sure how well it works)