app/views/layouts/_flash.html.erb
<div id="flash">
<% flash.each do |name, msg| %>
<%= content_tag :div, id: "flash_#{name}", class: "alert alert-info alert-dismissible fade in", role: 'alert' do %>
<%= msg.html_safe %>
<button type="button" class="close" data-dismiss="alert">
<span aria-hidden="true">×</span><span class="sr-only">Close</span>
</button>
<% end %>
<% end %>
</div>