Override core radios template to add class

agaric/templates/form/radios.html.twig

@@ -0,0 +1,13 @@
+{#
+/**
+ * @file
+ * Theme override for a 'radios' #type form element.
+ *
+ * Available variables
+ * - attributes: A list of HTML attributes for the wrapper element.
+ * - children: The rendered radios.
+ *
+ * @see template_preprocess_radios()
+ */
+#}
+<div{{ attributes.addClass('form-radios') }}>{{ children }}</div>