personal-course-rails7/app/views/admin/courses/new_assignment.html.erb

<%= form_for @course_assignment, url: create_assignment_admin_courses_path, html: {class: "form-horizontal main-forms previewable"} do |f| %>
  <fieldset>
    <%= render partial: 'form_assignment', locals: {f: f} %>
  </fieldset>
<% end %>