app/views/layouts/application.html.erb
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title><%= page_title %></title>
<%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => true %>
<%= javascript_include_tag 'application', 'data-turbolinks-track' => true %>
<%= csrf_meta_tags %>
</head>
<body>
<div class="navbar navbar-dark bg-dark">
<a href="/" class="navbar-brand">Buffer estimator</a>
<% if user_signed_in? %>
<ul class="nav navbar-nav navbar-right">
<li class="nav-item">
<%= link_to :destroy_user_session, class: "nav-link" do %>
<%= icon("sign-out", "Sign out") %>
<% end %>
</li>
</ul>
<% end %>
</div>
<% if notice %>
<div class="alert alert-info" role="alert"><%= notice %></div>
<% end %>
<% if alert %>
<div class="alert alert-warning" role="alert"><%= alert %></div>
<% end %>
<div class="container">
<%= yield %>
</div>
</body>
</html>