app/views/shared/_messages.html.erb
<% if flash[:error].present? %>
<div class="error">
<% flash.keys.each do |key| %>
<%= flash[key] %>
<% end %>
</div>
<% end %>
<% if flash[:notice].present? %>
<div class="notice">
<% flash.keys.each do |key| %>
<%= flash[key] %>
<% end %>
</div>
<% end %>