🧹 Narrow specificity of CSS selector

The selector was *very* specific, and with the HTML class changes for
Bootstrap 3 to 4, this almost certainly broke.

Note, there are still underlying issues with two other specs; there
errors are listed below:

```
1) Admin can select home page theme when a search results theme is
selected updates the search results page with the selected layout view

Failure/Error: super

     ActionView::Template::Error:
       undefined method `with_collection' for nil:NilClass
```

spec/features/appearance_theme_spec.rb

@@ -139,7 +139,7 @@
       allow_any_instance_of(ApplicationController).to receive(:current_account).and_return(account)
       visit '/'
       expect(page).to have_css('body.cultural_repository')
-      expect(page).to have_css('nav.navbar.navbar-inverse.navbar-static-top.cultural-repository-nav')
+      expect(page).to have_css('nav.navbar.cultural-repository-nav')
     end
 
     it 'updates the home theme when the theme is changed' do # rubocop:disable RSpec/ExampleLength
@@ -154,7 +154,7 @@
       allow_any_instance_of(ApplicationController).to receive(:current_account).and_return(account)
       visit '/'
       expect(page).to have_css('body.cultural_repository')
-      expect(page).to have_css('nav.navbar.navbar-inverse.navbar-static-top.cultural-repository-nav')
+      expect(page).to have_css('nav.navbar.cultural-repository-nav')
       visit '/admin/appearance'
       click_link('Themes')
       select('Default home', from: 'Home Page Theme')
@@ -174,7 +174,7 @@
       visit '/'
       expect(page).to have_css('body.missing_theme')
       expect(page).not_to have_css('nav.cultural-repsitory-nav')
-      expect(page).to have_css('nav.navbar.navbar-inverse.navbar-static-top')
+      expect(page).to have_css('nav.navbar.navbar-expand-lg')
     end
   end
 end