Give wrapping section and div for highlight region blocks

agaric/templates/block/block--highlighted.html.twig

@@ -0,0 +1,20 @@
+{# See "@stable/block/block.html.twig" #}
+{%
+  set classes = [
+    'hero',
+    'is-light',
+  ]
+%}
+{% set attributes = attributes.addClass(classes).addAttribute('data-headerbg', 'light') %}
+<section{{ attributes }}>
+  <div class="hero-body subtitle is-mono is-4">
+    {{ title_prefix }}
+    {% if label %}
+      <h2{{ title_attributes }}>{{ label }}</h2>
+    {% endif %}
+    {{ title_suffix }}
+    {% block content %}
+      {{ content }}
+    {% endblock %}
+  </div>
+</section>