bootstrap 4 navbar not working in rails 5 app

I’m migrating my static HTML/CSS/JS site to a Rails app. I’m using Bootstrap 4, and all the Bootstrap 4 functionality and CSS classes were working on the static page. Now in the Ruby app, the navbar isn’t showing up at all.

Am I missing a gem file? Is there a specific way to embed the style tags that I’m doing wrong?

my gem file:

gem 'rails', '~> 5.0.5'
gem 'sqlite3'
gem 'puma', '~> 3.0'
gem 'sass-rails', '~> 5.0'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.2'
gem 'bootstrap', '~> 4.0.0.beta'
gem 'font-awesome-rails', '~> 4.7', '>= 4.7.0.2'
gem "autoprefixer-rails"
gem 'jquery-rails'
gem 'turbolinks', '~> 5'
gem 'jbuilder', '~> 2.5'
group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a 
debugger console
  gem 'byebug', platform: :mri
end

group :development do
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '~> 3.0.5'
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

my javascript requires:

//= require jquery
//= require bootstrap
//= require jquery_ujs
//= require turbolinks
//= require_tree .

my custom CSS:

.navbar-custom {
  border-radius: 0px;
  z-index: 16;
  box-shadow: 0 2px 3px 0 rgba(0,0,0, .4);
}

my application.html.erb head:

<%= stylesheet_link_tag    'application', media: 'all', 'data-
turbolinks-track': 'reload' %>
<%= javascript_include_tag 'application', 'data-turbolinks-track': 
'reload' %>

my application.html.erb navbar:

<nav class="navbar navbar-toggleable-md navbar-inverse bg-inverse navbar-custom">
  <div class="container-fluid d-inline-flex">

    <button type="button" class="navbar-toggler navbar-toggler-right" data-toggle="collapse" data-target="#navbarSupportedContent" aria-expanded="false">
      <span class="sr-only">Toggle navigation</span>
      <span class="navbar-toggler-icon"></span>
      <a class="navbar-brand justify-cotent-start" target="_blank" rel="nofollow" href="#home"><%= image_tag "logo.png", size:"50" %></a>
    </button>

    <a class="navbar-brand justify-cotent-start" target="_blank" rel="nofollow" href="#home"><%= image_tag "logo.png", size:"50" %></a>
    <div class="collapse navbar-collapse justify-content-end" id="navbarSupportedContent">
      <ul class="nav navbar-nav ml-auto" style="float: right">
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#about">about</a></li>
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#events">events</a></li>
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#gallery">gallery</a></li>
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#music">music</a></li>
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#press-kit">press kit</a></li>
        <li class="nav-item"><a class="nav-link" target="_blank" rel="nofollow" href="#contact">contact</a></li>
      </ul>
    </div>
  </div>
</nav>