app/views/layouts/_messages.html.erb
<div class="row">
<div class="col-xs-10 col-xs-offset-1">
<% flash.each do |name, message| %>
<div class='alert alert-<%="#{name}"%>'>
<a href="#" class="close" data-dismiss="alert">×</a>
<%= content_tag :div, message, id: "flash_#{name}" if message.is_a?(String) %>
</div>
<% end %>
</div>
</div>