Index: wp-includes/blocks/buttons/style.css
===================================================================
--- wp-includes/blocks/buttons/style.css	(revision 53465)
+++ wp-includes/blocks/buttons/style.css	(working copy)
@@ -111,16 +111,26 @@
 .wp-block-buttons.aligncenter {
   text-align: center;
 }
+.wp-block-buttons.alignright {
+  text-align: right;
+}
 .wp-block-buttons:not(.is-content-justification-space-between,
 .is-content-justification-right,
 .is-content-justification-left,
-.is-content-justification-center) .wp-block-button.aligncenter {
+.is-content-justification-center) .wp-block-button.aligncenter, 
+.wp-block-buttons:not(.is-content-justification-space-between,
+.is-content-justification-right,
+.is-content-justification-left,
+.is-content-justification-center) .wp-block-button.alignright
+{
   /* stylelint-enable indentation */
   margin-left: auto;
   margin-right: auto;
   width: 100%;
 }
-
 .wp-block-button.aligncenter {
   text-align: center;
+}
+.wp-block-button.alignright {
+  text-align: right;
 }
\ No newline at end of file