{% block content %}
{% form_theme form 'bootstrap_3_layout.html.twig' %}
.....
{% endblock %}
{% block form_label %}
{% set label_attr = label_attr|merge({class: ('mb-10')|trim}) %}
{{ parent() }}
{% endblock form_label %}
Reusing Parts of a Built-In Form Theme
Finally, you can also use the Twig parent() function to reuse the original content of the built-in theme. This is useful when you only want to make minor changes, such as wrapping the generated HTML with some element:{% use 'form_div_layout.html.twig' %} {% block integer_widget %} <div class="some-custom-class"> {{ parent() }} </div> {% endblock %}