<div id="dropbox_modal" class="modal hide big-modal" tabindex="-1" role="dialog" aria-labelledby="dropbox_modal_label">
  <%= form_tag(master_files_path) do -%>
    <div class="modal-header">
      <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    </div>
    <div class="modal-body">
      <%= render partial: "dropbox_file_navigator", locals: {file_set: @dropbox_files} %>
    </div>
    <div class="modal-footer">
      <p style="clear:both">
        <%= link_to 'Remove Selected Files', bulk_delete_dropbox_index_path, class: 'btn btn-danger pull-left remove-selected-files' %>
        <%= button_tag "Close", type: "button", class: "btn", 'data-dismiss'=>'modal' %>
        <%= button_tag "Attach Selected Files", class: "btn", donot_advance: true %>
      </p>
    </div>
  <% end %>
</div>

<div id="dropbox_modal" class="modal hide fade big-modal" tabindex="-1" role="dialog" aria-labelledby="dropbox_modal_label">
  <%= form_tag(master_files_path) do -%>
    <div class="modal-header">
      <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    </div>
    <div class="modal-body">
      <%= render partial: "dropbox_file_navigator", locals: {file_set: @dropbox_files} %>
    </div>
    <div class="modal-footer">
      <p style="clear:both">
        <%= link_to 'Remove Selected Files', bulk_delete_dropbox_index_path, class: 'btn btn-danger pull-left remove-selected-files' %>
        <%= button_tag "Close", type: "button", class: "btn", 'data-dismiss'=>'modal' %>
        <%= button_tag "Attach Selected Files", class: "btn", donot_advance: true %>
      </p>
    </div>
  <% end %>
</div>

Add fade class to dropbox modal
Add fade class to dropbox modal
