Index: wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css
===================================================================
--- wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css	(revision 54300)
+++ wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css	(working copy)
@@ -794,6 +794,7 @@
 	padding: 0;
 	position: relative;
 	text-align: center;
+	border-style: solid;
 }
 
 .editor-styles-wrapper .wp-block-pullquote::before {
Index: wp-content/themes/twentytwenty/assets/css/editor-style-block.css
===================================================================
--- wp-content/themes/twentytwenty/assets/css/editor-style-block.css	(revision 54300)
+++ wp-content/themes/twentytwenty/assets/css/editor-style-block.css	(working copy)
@@ -798,6 +798,7 @@
 	padding: 0;
 	position: relative;
 	text-align: center;
+	border-style: solid;
 }
 
 .editor-styles-wrapper .wp-block-pullquote::before {