app/views/spree/admin/shipping_matrices/new.html.erb
<%= render 'spree/shared/error_messages', target: @shipping_matrix %>
<%= form_for [:admin, @shipping_matrix] do |f| %>
<fieldset>
<legend align="center"><%= Spree.t(:new, scope: :shipping_matrix) %></legend>
<%= render 'form', f: f %>
<%= render 'spree/admin/shared/new_resource_links' %>
</fieldset>
<% end %>