app/views/layouts/_flash_messages.html.erb
<div id='flash-messages'>
<%- if flash.notice.present? %>
<div class="alert alert-success">
<button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
<%= flash.notice %>
</div>
<%- end %>
<%- if flash.alert.present? %>
<div class="alert alert-warning">
<button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
<%= flash.alert %>
</div>
<%- end %>
<%- if flash.key? :error %>
<div class="alert alert-danger">
<button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
<%= flash[:error] %>
</div>
<%- end %>
</div>