application.js

//= require jquery
//= require jquery_ujs
//= require twitter/bootstrap
//= require rails.validations.simple_form
//= require_tree .
//= require_self

bootstrapfix.js

(function() {
    $(document).ready(function() {
        return $("div.control-group").focusout(function() {
            if (!$("div.control-group").hasClass("error")) {
                return $(this).addClass("success");
            }
        });
    });
}).call(this);

ClientSideValidations.formBuilders['SimpleForm::FormBuilder'] = {
    add: function(element, settings, message) {
        var errorElement, wrapper;

        settings.wrapper_tag = ".control-group";
        settings.error_tag = "span";
        settings.error_class = "help-inline";
        settings.wrapper_error_class = "error";
        settings.wrapper_success = "success";

        if (element.data('valid') !== false) {
            wrapper = element.closest(settings.wrapper_tag);
            wrapper.removeClass(settings.wrapper_success);
            wrapper.addClass(settings.wrapper_error_class);
            errorElement = $("<" + settings.error_tag + "/>", {
                "class": settings.error_class,
                text: message
            });
            return wrapper.find(".controls").append(errorElement);
        } else {
            wrapper = element.closest(settings.wrapper_tag);
            wrapper.addClass(settings.wrapper_error_class);
            return element.parent().find("" + settings.error_tag + "." + settings.error_class).text(message);
        }
    },
    remove: function(element, settings) {
        var errorElement, wrapper;

        settings.wrapper_tag = ".control-group";
        settings.error_tag = "span";
        settings.error_class = "help-inline";
        settings.wrapper_error_class = "error";
        settings.wrapper_success = "success";

        wrapper = element.closest("" + settings.wrapper_tag + "." + settings.wrapper_error_class);
        wrapper.removeClass(settings.wrapper_error_class);
        wrapper.addClass(settings.wrapper_success);
        errorElement = wrapper.find("" + settings.error_tag + "." + settings.error_class);
        return errorElement.remove();
    }
};

widok.html.erb

<%= simple_form_for @wallet, validate: true, url: create_budget_path, html: {class: "form-horizontal"} do |f| %>
    <%= f.input :name, label: 'Budget name' %>
    <%= f.input :amount, wrapper: :append, wrapper_html: {id: 'budget_amount'} do %>
      <%= f.input_field :amount, as: :currency %>
    <% end %>

    <div id="budget_plan">
      <%= f.simple_fields_for :expenses do |builder| %>
        <%= render "expenses/expenses_fields", f: builder %>
      <% end %>
      <div><%= link_to_add_fields "Add Expense", f, :expenses %></div>
    </div>

    <div class="form-actions">
      <%= f.button :submit, 'Add budget', class: 'btn btn-primary' %>
      <%= link_to "Plan this budget", "#", id: "budget_plan_link", class: "btn" %>
    </div>
<% end %>