diff --git a/wp-includes/js/thickbox/thickbox.css b/wp-includes/js/thickbox/thickbox.css
index 6bfac61ee4..3374f68569 100644
--- a/wp-includes/js/thickbox/thickbox.css
+++ b/wp-includes/js/thickbox/thickbox.css
@@ -145,3 +145,12 @@
 #TB_closeWindowButton:focus .tb-close-icon {
 	color: #00a0d2;
 }
+
+#TB_closeWindowButton:focus .tb-close-icon {
+	-webkit-box-shadow:
+		0 0 0 1px #5b9dd9,
+		0 0 2px 1px rgba(30, 140, 190, .8);
+	box-shadow:
+		0 0 0 1px #5b9dd9,
+		0 0 2px 1px rgba(30, 140, 190, .8);
+}
diff --git a/wp-includes/js/thickbox/thickbox.js b/wp-includes/js/thickbox/thickbox.js
index 164f72e616..391fd4186e 100644
--- a/wp-includes/js/thickbox/thickbox.js
+++ b/wp-includes/js/thickbox/thickbox.js
@@ -212,7 +212,7 @@ function tb_show(caption, url, imageGroup) {//function called when the user clic
 			}else{// not an iframe, ajax
 					if(jQuery("#TB_window").css("visibility") != "visible"){
 						if(params['modal'] != "true"){//ajax no modal
-						jQuery("#TB_window").append("<div id='TB_title'><div id='TB_ajaxWindowTitle'>"+caption+"</div><div id='TB_closeAjaxWindow'><a href='#' id='TB_closeWindowButton'><div class='tb-close-icon'></div></a></div></div><div id='TB_ajaxContent' style='width:"+ajaxContentW+"px;height:"+ajaxContentH+"px'></div>");
+						jQuery("#TB_window").append("<div id='TB_title'><div id='TB_ajaxWindowTitle'>"+caption+"</div><div id='TB_closeAjaxWindow'><button type='button' id='TB_closeWindowButton'><span class='screen-reader-text'>"+thickboxL10n.close+"</span><span class='tb-close-icon'></span></button></div></div><div id='TB_ajaxContent' style='width:"+ajaxContentW+"px;height:"+ajaxContentH+"px'></div>");
 						}else{//ajax modal
 						jQuery("#TB_overlay").unbind();
 						jQuery("#TB_window").append("<div id='TB_ajaxContent' class='TB_modal' style='width:"+ajaxContentW+"px;height:"+ajaxContentH+"px;'></div>");
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6ff80d420f..1b24dcafd2 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-alpha-37530';
+$wp_version = '4.6-alpha-37531';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.