views/macros/alert.html.twig
{% macro alert(type, message, id, class, close) %}
<div class="alert{{ type ? ' alert-'~type : '' }} fade in {{ class|default('') }} {% if close|default(false) %}alert-dismissable{% endif %}">
{% if close|default(false) %}
<button type="button" class="close" data-dismiss="alert" aria-hidden="true">×</button>
{% endif %}
{{ message|raw }}
</div>
{% endmacro %}