bootstrap not working on rails 4 : i'm having problems with my app,i can't see any bootstraps effects on my rails app it looks the same. i have done bundle install,but i can't see any difference in it.this is my first time using bootstrap
here is my gemfile

   

     source 'https://rubygems.org'
    
    
    # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
    gem 'rails', '4.2.5.1'
    gem 'bootstrap-sass', '~> 3.3.6'
    gem 'sass-rails', '~> 5.0'
    # Use Uglifier as compressor for JavaScript assets
    gem 'uglifier', '>= 1.3.0'
    # Use CoffeeScript for .coffee assets and views
    gem 'coffee-rails', '~> 4.1.0'
    # See https://github.com/rails/execjs#readme for more supported runtimes
    # gem 'therubyracer', platforms: :ruby
    
    # Use jquery as the JavaScript library
    gem 'jquery-rails'
    # Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
    gem 'turbolinks'
    # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
    gem 'jbuilder', '~> 2.0'
    # bundle exec rake doc:rails generates the API under doc/api.
    gem 'sdoc', '~> 0.4.0', group: :doc
    
    # Use ActiveModel has_secure_password
    # gem 'bcrypt', '~> 3.1.7'
    
    # Use Unicorn as the app server
    # gem 'unicorn'
    
    # Use Capistrano for deployment
    # gem 'capistrano-rails', group: :development
    
    group :development, :test do
      gem 'sqlite3'
      # Call 'byebug' anywhere in the code to stop execution and get a debugger console
      gem 'byebug'
    end
    
    group :development do
      # Access an IRB console on exception pages or by using <%= console %> in views
      gem 'web-console', '~> 2.0'
    
      # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
      gem 'spring'
    end
    
    group :production do
      gem 'pg'
      gem 'rails_12factor'
      
    and my application js
    // 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 any plugin's vendor/assets/javascripts directory 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
    // compiled file.
    //
    // Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
    // about supported directives.
    //
    //= require jquery
    //= require jquery_ujs
    //= require bootstrap-sprockets
    //= require turbolinks
    //= require_tree .
    
    and my application css
    This is a manifest file that'll be compiled into application.css, which will include all the files
     * listed below.
     *
     * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
     * or any plugin's vendor/assets/stylesheets directory can be referenced here using a relative path.
     *
     * You're free to add application-wide styles to this file and they'll appear at the bottom of the
     * compiled file so the styles you add here take precedence over styles defined in any styles
     * defined in the other CSS/SCSS files in this directory. It is generally better to create a new
     * file per style scope.
     *
     *= require_tree .
     *= require_self

 */
