Component

container--more-link.html.twig

{% extends '/themes/THEME/components/container.twig' %}
  {% block content %}
    <div{{ attributes.addClass(classes, add_classes).removeClass(remove_classes) }}>
      {{ children }}
    </div>
  {% endblock %}

container.twig

{# Core Classes  #}
{%
  set classes = [
    has_parent ? 'js-form-wrapper',
    has_parent ? 'form-wrapper',
  ]
%}
{# Map #type to theme component #}
{%
  set map = {
    'more_link': 'btn',
  }
%}
{% set remove_classes = [] %}
{% set add_classes = [] %}
{% for key,value in map %}
  {# Prefer component classes instead of defaults when a match is present, e.g.
    - Add: .btn btn--more-link
    - Remove: .more-link
  #}
  {% if element['#type'] == key %}
    {# Add component classes. #}
    {% set add_classes = [
        value,
        value ~ '--' ~ key|clean_class,
    ] %}

    {# Remove the original base #type class. #}
    {% set remove_classes = [ key|clean_class ] %}

  {% endif %}
{% endfor %}

{% block content %}
{% endblock %}