Hi  ☒ ,
Oops, I didn't. Only had:
<%= stylesheet_link_tag 'application',
          media: 'all',
          'data-turbolinks-track': 'reload' %>

    <%= javascript_pack_tag 'application',
          'data-turbolinks-track': 'reload',
          defer: true %>

Added the line <%= stylesheet_pack_tag 'application' %> and now it works.

Thank you very much for your help