simplytest-8.x-4.x-dev/themes/simplytest_theme/templates/block/block.html.twig

{% block block_classes %}
  {% set classes = ['block', attributes.id|clean_class] %}
  {% set attributes = attributes.addClass(classes) %}
{% endblock %}
<div{{ attributes }}>
  {{ title_prefix }}
  {% if label %}
    <h2{{ title_attributes.addClass('block__title') }}>{{ label }}</h2>
  {% endif %}
  {{ title_suffix }}
  {% block content %}
    {{ content }}
  {% endblock %}
</div>