Spree Multi Theme is a standalone theme for Spree Commerce version 1.1.0.
This theme is now being used as the base theme for SpreeUI demo store:
Add the following line to your Gemfile:
gem 'spree_multi_theme', :git => 'firstname.lastname@example.org:railsfactory/spree_multi_theme.git'
NOTE: It's important that you add this line at the bottom of the Gemfile, or at least AFTER any other extension/engine/gem that you'd like to use the theme (i.e. Spree)
$ bundle install
Then Start The servers:
$ rails s
Optional: Clear out precompiled assets (required for install in sandbox):
$ rake assets:clean
Following the link "http://spreeui.railsfactory.com/admin" You can see the Theme tab according to the theme list you can select the theme.