ungleich-user/dal/templates/includes/_messages.html

{% if messages %}
    <ul class="list-unstyled msg-list">
    {% for message in messages %}
        <div class="alert {% if message.tags and message.tags == 'error' %} alert-danger {% else %} alert-{{message.tags}} {% endif %}">{{ message|safe }}</div>
    {% endfor %}
    </ul>
{% endif %}