Start with default generated template

templates/block/block--local-actions-block.html.twig

@@ -0,0 +1,12 @@
+{% extends "block.html.twig" %}
+{#
+/**
+ * @file
+ * Theme override for local actions (primary admin actions.)
+ */
+#}
+{% block content %}
+  {% if content %}
+    <nav class="action-links">{{ content }}</nav>
+  {% endif %}
+{% endblock %}