Index: src/wp-admin/css/themes.css
===================================================================
--- src/wp-admin/css/themes.css	(revision 31480)
+++ src/wp-admin/css/themes.css	(working copy)
@@ -525,6 +525,7 @@
 	-webkit-box-sizing: border-box;
 	-moz-box-sizing: border-box;
 	box-sizing: border-box;
+	-webkit-overflow-scrolling: touch;
 }
 
 .theme-overlay .theme-wrap:after {
@@ -924,7 +925,7 @@
 		left: 0;
 		padding: 70px 20px 20px;
 		border: none;
-		z-index: 500; /* should overlap #wpadminbar, which is 500 on mobile. */
+		z-index: 100000; /* should overlap #wpadminbar. */
 		position: fixed;
 	}