Index: wp-content/themes/twentytwentyone/style.css
===================================================================
--- wp-content/themes/twentytwentyone/style.css	(revision 56024)
+++ wp-content/themes/twentytwentyone/style.css	(working copy)
@@ -2942,7 +2942,7 @@
 	}
 }
 
-.wp-block-quote {
+.wp-block-quote.is-style-plain {
 	border-left: none;
 
 	/**