Use visible texts in tests

Content like lowercase letters with `text-transform: uppercase` or
spaces after elements with `display: block` or "You're on page:" are not
seen that way by users with a browser supporting CSS.

So we're testing what most users actually experience.

spec/system/site_customization/custom_pages_spec.rb

@@ -87,13 +87,13 @@ describe "Custom Pages" do
         expect(page).to have_content("Subtitle for custom page")
       end
 
-      scenario "Show widget cards for that page" do
+      scenario "Show widget cards for that page", :js do
         custom_page = create(:site_customization_page, :published)
         create(:widget_card, cardable: custom_page, title: "Card Highlights")
 
         visit custom_page.url
 
-        expect(page).to have_content "Card Highlights"
+        expect(page).to have_content "CARD HIGHLIGHTS"
       end
     end
   end