Paper is a implementation of Flx Design System for Flutter.
Add a lines like this to your pubspec.yaml.
dependencies: paper: git: url: https://github.com/the-flx/paper.git ref: vX.X.X
After replace X.X.X of the prefer version of package on github releases page.
Next step is will run command
flutter pub get.
Now in your Dart code, import paper like on example.