Index: src/wp-content/themes/twentytwelve/css/editor-blocks.css
===================================================================
--- src/wp-content/themes/twentytwelve/css/editor-blocks.css	(revision 59949)
+++ src/wp-content/themes/twentytwelve/css/editor-blocks.css	(working copy)
@@ -141,6 +141,7 @@
 
 /* Captions */
 
+[class*=" wp-block-"] figcaption,
 [class^="wp-block-"] figcaption,
 [class^="wp-block-"] figcaption.editor-rich-text__tinymce.mce-content-body {
 	color: #757575;
@@ -147,14 +148,9 @@
 	font-size: 12px;
 	line-height: 2;
 	font-style: italic;
-	text-align: left;
+	text-align: start;
 }
 
-.rtl [class^="wp-block-"] figcaption,
-.rtl [class^="wp-block-"] figcaption.editor-rich-text__tinymce.mce-content-body {
-	text-align: right;
-}
-
 /* Definition Lists */
 
 .wp-block-freeform.block-library-rich-text__tinymce dt {