Datepicker not showing proper field

I’m using Rails version 3.2 and Ruby 1.9.3

I’m trying to make within a form_tag a datepicker field.
In my GemFile I have added gem ‘jquery-rails’ and gem ‘jquery_datepicker’.
In the rails console I have used the command: rails generate jquery:install --ui

Application.js looks like this:

// This is a manifest file that'll be compiled into application.js, which will include all the files
// listed below.
//
// Any JavaScript/Coffee file within this directory, lib/assets/javascripts, vendor/assets/javascripts,
// or vendor/assets/javascripts of plugins, if any, can be referenced here using a relative path.
//
// It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
// the compiled file.
//
// WARNING: THE FIRST BLANK LINE MARKS THE END OF WHAT'S TO BE PROCESSED, ANY BLANK LINE SHOULD
// GO AFTER THE REQUIRES BELOW.
//
//= require jquery
//= require jquery_ujs
//= require jquery_ui
//= require jquery-ui-timepicker-addon.js
//= require_tree .

Application.css:

/*
 * This is a manifest file that 'll be compiled into application.css, which will include all the files
* listed below.

I think you have to add script for datepicker
Just like below

$(function() {

$(".date_picker").datepicker({

dateFormat : ‘d M, yy’,

minDate : 0,

maxDate : +90

});

});