change header background

templates/html.tpl.php

@@ -79,8 +79,8 @@
 
     	<style type="text/css" id="twentythirteen-header-css">
     			.site-header {
-    			background: url(<?php echo $GLOBALS['base_url'].'/'.drupal_get_path('theme', 'abims');?>/images/abims/abims.png) no-repeat scroll top;
-    			background-size: 500px auto;
+    			background: url(<?php echo $GLOBALS['base_url'].'/'.drupal_get_path('theme', 'abims');?>/images/abims/abims.png) no-repeat scroll center;
+    			background-size: 200px auto;
                         background-color: #297FD5
     		}
     		@media (max-width: 767px) {