Index: src/wp-admin/js/theme.js
===================================================================
--- src/wp-admin/js/theme.js	(revision 26862)
+++ src/wp-admin/js/theme.js	(working copy)
@@ -610,6 +610,7 @@
 
 	tagName: 'input',
 	className: 'theme-search',
+	id: 'theme-search-input',
 
 	attributes: {
 		placeholder: l10n.searchPlaceholder,