Index: wp-content/themes/twentynineteen/style-editor.css
===================================================================
--- wp-content/themes/twentynineteen/style-editor.css	(revision 53212)
+++ wp-content/themes/twentynineteen/style-editor.css	(working copy)
@@ -596,7 +596,7 @@
 body .wp-block[data-align="right"],
 body .wp-block.alignright {
   margin-left: 1rem;
-  width: inherit;
+  width: 100% !important;
 }
 
 body .wp-block[data-align="center"],
Index: wp-content/themes/twentynineteen/style-editor.scss
===================================================================
--- wp-content/themes/twentynineteen/style-editor.scss	(revision 53212)
+++ wp-content/themes/twentynineteen/style-editor.scss	(working copy)
@@ -26,7 +26,7 @@
 	.wp-block[data-align="right"],
 	.wp-block.alignright {
 		margin-left: $size__spacing-unit;
-		width: inherit;
+		width: 100% !important;
 	}
 
 	.wp-block[data-align="center"],