Index: src/wp-content/themes/twentyfifteen/style.css
===================================================================
--- src/wp-content/themes/twentyfifteen/style.css	(revision 30950)
+++ src/wp-content/themes/twentyfifteen/style.css	(working copy)
@@ -622,7 +622,12 @@
 	padding: 0;
 }
 
+.search-form input[type="submit"],
+.widget .search-form input[type="submit"] {
+	padding: 0;
+}
 
+
 /**
  * 6.0 Navigations
  */