Index: wp-content/themes/twentythirteen/style.css
===================================================================
--- wp-content/themes/twentythirteen/style.css	(revision 23695)
+++ wp-content/themes/twentythirteen/style.css	(working copy)
@@ -388,6 +388,7 @@
 input[type="search"] {
 	-webkit-appearance: textfield;
 	padding-right: 2px; /* Don't cut off the webkit search cancel button */
+	width: 270px;
 }
 
 input[type="search"]::-webkit-search-decoration {