Removing reference to  global/all.css from engine.rb - this was added to test a attempt to resolve an asset precompilation error and is not required - it was not part of the original spree code
The following has been added in order to fix various asset precompilation issues due to undefined variables. The fix is to ensure that the variables declared in scss partials in the globals directory are available to the other scss files that require them.  This is intended to be a temporary fix - there are imports for these files in spree_admin.scss and ideally this should work and we should not have to add imports to multiple files