Start with default generated template

templates/dataset/item-list--search-results.html.twig

@@ -0,0 +1,29 @@
+{% extends "item-list.html.twig" %}
+{#
+/**
+ * @file
+ * Theme override for an item list of search results.
+ *
+ * Available variables:
+ * - items: A list of items. Each item contains:
+ *   - attributes: HTML attributes to be applied to each list item.
+ *   - value: The content of the list element.
+ * - title: The title of the list.
+ * - list_type: The tag for list element ("ul" or "ol").
+ * - attributes: HTML attributes to be applied to the list.
+ * - empty: A message to display when there are no items. Allowed value is a
+ *   string or render array.
+ * - context: An list of contextual data associated with the list. For search
+ *   results, the following data is set:
+ *   - plugin: The search plugin ID, for example "node_search".
+ *
+ * @see template_preprocess_item_list()
+ */
+#}
+{%
+  set classes = [
+    'search-results',
+    context.plugin ~ '-results',
+  ]
+%}
+{% set attributes = attributes.addClass(classes) %}