Use indigo as default theme

lib/gitlab/themes.rb

@@ -5,7 +5,7 @@ module Gitlab
     extend self
 
     # Theme ID used when no `default_theme` configuration setting is provided.
-    APPLICATION_DEFAULT = 2
+    APPLICATION_DEFAULT = 1
 
     # Struct class representing a single Theme
     Theme = Struct.new(:id, :name, :css_class)

spec/helpers/preferences_helper_spec.rb

@@ -37,9 +37,9 @@ describe PreferencesHelper do
       it 'returns the default when id is invalid' do
         stub_user(theme_id: Gitlab::Themes.count + 5)
 
-        allow(Gitlab.config.gitlab).to receive(:default_theme).and_return(2)
+        allow(Gitlab.config.gitlab).to receive(:default_theme).and_return(1)
 
-        expect(helper.user_application_theme).to eq 'ui_dark'
+        expect(helper.user_application_theme).to eq 'ui_indigo'
       end
     end
 

spec/models/user_spec.rb

@@ -727,7 +727,7 @@ describe User do
       it "applies defaults to user" do
         expect(user.projects_limit).to eq(123)
         expect(user.can_create_group).to be_falsey
-        expect(user.theme_id).to eq(2)
+        expect(user.theme_id).to eq(1)
       end
     end