How to remove the background in Exception Handler gem in Rails 5?

Question

I am trying to add this gem https://github.com/richpeck/exception_handler to my website.

This is my config/application.rb

 config.exception_handler = {
            dev: true,
            db:     false, #-> defaults to :errors if true, else use :table_name
            email:  false, #-> need to integrate
            layouts: {
                '404' => 'application',
                '400' => 'application',
                '500' => 'application'
            },
    }

This is my app/views/exception_handler/exception/show.html.erb

<% provide(:title, 'Error') %>

<div class="jumbotronsignup nopadding">
  <div class="container nopadding">
    <div class="row">

        <% if /^(5[0-9]{2})$/ =~ @exception.status.to_s %>  

          <div class="col-md-4 col-md-offset-4 labelcolor padding2">

            <h3><%= "#{@exception.status} Error - #{details[:name]}" %></h3>
            <%= details[:description] %>
            <div class="thumbnail">
                        <strong>Our developers have been notified - we're working on it!</strong>
            </div>

           </div>

            <% else %>

          <div class="col-md-4 col-md-offset-4 labelcolor padding2">

            <div class="thumbnail">
                        <strong><%= content_tag :div, details[:description], class: "message" %></strong>
            </div>

           </div>

            <% end %>

    </div>

  </div>
</div>

I haven't changed the app/controllers/exception_handler/exception_controller.rb and app/helpers/exception_handler/application_helper.rb I don't know why that background image is getting displayed.

If I delete the contents of app/assets/stylesheets/exception_handler/error.css.erb, then the image goes away and the content gets displayed as I want.

Where do I change to get that image away?