Index: wp-content/themes/twentyeleven/style.css
===================================================================
--- wp-content/themes/twentyeleven/style.css	(revision 53690)
+++ wp-content/themes/twentyeleven/style.css	(working copy)
@@ -2851,3 +2851,12 @@
 #ie8 section.featured-post .attachment-small-feature {
 	max-width: none;
 }
+
+
+/* Button Block
+----------------------------------------------- */
+
+.wp-block-button.alignright {
+	text-align: right;
+	width: 100%;
+}