app/views/layouts/_flash.html.erb
<% flash.each do |flash_key, flash_message| %>
<div id="<%= flash_key %>" data-alert class="notice-container callout-slide" data-closable>
<div class="callout notice <%= flash_key %>">
<button class="close-button" aria-label="<%= t("application.close") %>" type="button" data-close>
<span aria-hidden="true">×</span>
</button>
<div class="notice-text">
<%= sanitize(flash_message) %>
</div>
</div>
</div>
<% end %>