app/views/customers/_form.html.erb
<div>
<%= form_for customer do |f| %>
<%= render "errors", object: customer %>
<div class="form-group">
<%= f.label :first_name %>
<%= f.text_field :first_name, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :last_name %>
<%= f.text_field :last_name, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :email %>
<%= f.text_field :email, class: "form-control" %>
</div>
<div>
<%= f.submit "Submit", class: "btn btn-primary"%>
</div>
<% end %>
</div>