Override template for blocks in bottom content region

agaric/templates/block/block--content-bottom.html.twig

@@ -0,0 +1,10 @@
+{% extends '@bulma/block/block.html.twig' %}
+{% set view_mode = configuration['view_mode'] ?? null %}
+{% if view_mode is same as ('columnar') %}
+  {%
+    set classes = [
+      'column'
+    ]
+  %}
+  {% set attributes = attributes.addClass(classes) %}
+{% endif %}