Index: src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
===================================================================
--- src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(revision 27765)
+++ src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(working copy)
@@ -41,7 +41,10 @@
 }
 
 .html5-captions .wp-caption {
-	padding: 4px;
+	border: none;
+	background-color: transparent;
+	margin: 0;
+	padding: 0;
 }
 
 .mceIEcenter {