flash[:alert] = "You must be logged in."
flash[:notice] = "Post successfully created."
Display
<p class="notice"><%= flash[:notice] %></p>
<p class="alert"><%= flash[:alert] %></p>
Styling
app/views/layouts/application.html.erb
<%= render partial: "layouts/flash" %>
app/views/layouts/_flash.html.erb
<% flash.each do |type, message| %>
<div>
<%= message %>
</div>
<% end %>