Spree Backendx spreads the new Spree UX frontend styles to the backend. RoR extension for Spree 4.1 ready
Add this line to your application's Gemfile:
gem 'spree_backendx', github: 'MateoLa/spree_backendx'
And then execute:
$ bundle install
$ bundle exec rails g spree_backendx:install
The gem is available as open source under the terms of the MIT License.