wagtail_bakerydemo/bakerydemo/templates/includes/messages.html

{% if messages %}
    <div role="alertdialog">
        <ul class="messages">
            {% for message in messages %}
            <li{% if message.tags %} class="{{ message.tags }}"{% endif %} role="alert">{{ message }}</li>
            {% endfor %}
        </ul>
    </div>
{% endif %}