{% form_theme form _self %} {% block checkbox_widget -%} {%- set parent_label_class = parent_label_class|default(label_attr.class|default('')) -%} {%- if 'checkbox-custom' in parent_label_class -%} {%- set attr = attr|merge({class: (attr.class|default('') ~ ' custom-control-input')|trim}) -%}