Index: src/wp-admin/css/common.css
===================================================================
--- src/wp-admin/css/common.css	(revision 55106)
+++ src/wp-admin/css/common.css	(working copy)
@@ -3030,11 +3030,18 @@
 
 .plugin-details-modal #TB_closeWindowButton:hover,
 .plugin-details-modal #TB_closeWindowButton:focus {
-	color: #135e96;
+	color: #f0f0f1;
 	outline: none;
 	box-shadow: none;
 }
 
+.plugin-details-modal #TB_closeWindowButton:hover::after,
+.plugin-details-modal #TB_closeWindowButton:focus::after {
+	outline: 2px solid;
+	outline-offset: -4px;
+	border-radius: 4px;
+}	
+
 .plugin-details-modal .tb-close-icon {
 	display: none;
 }