Index: wp-admin/css/themes.css
===================================================================
--- wp-admin/css/themes.css	(revision 31604)
+++ wp-admin/css/themes.css	(working copy)
@@ -916,7 +916,7 @@
 @media only screen and (max-width: 780px) {
 	body.folded .theme-overlay .theme-wrap,
 	.theme-overlay .theme-wrap {
-		top: 0; /* The adminmenu isn't fixed on mobile, so this can use the full viewport height */
+		top: 46px; /* Top value should equal to #wpadminbar height */
 		right: 0;
 		bottom: 0;
 		left: 0;