obdev/app/views/users/_form.html.erb

<%= form_with(model: user, local: true, html: { class: 'needs-validation', novalidate: true }) do |form| %>
  <!-- Display errors, if any -->
  <% if user.errors.any? %>
    <div id="error_explanation" class="alert alert-danger" role="alert">
      <h4><%= pluralize(user.errors.count, "error") %> prohibited this user from being saved:</h4>
      <ul>
        <% user.errors.full_messages.each do |message| %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <!-- Email field -->
  <div class="mb-3">
    <%= form.label :email, class: 'form-label' %>
    <%= form.email_field :email, id: :user_email, class: 'form-control' %>
  </div>

  <!-- Role selection -->
  <div class="mb-3">
    <%= form.label :roles, 'Assign Role', class: 'form-label' %>
    <%= form.select :roles, options_for_select(Role.pluck(:name), user.roles.pluck(:name)), {}, { multiple: true, class: 'form-control' } %>
  </div>

  <!-- Submit button -->
  <div class="actions">
    <%= form.submit 'Save', class: 'btn btn-dark' %>
  </div>
<% end %>