Accessibility: Improve color contrast updating any #999 gray used for text or icons to a darker gray.

Fixes #35660.
Built from https://develop.svn.wordpress.org/trunk@36587


git-svn-id: http://core.svn.wordpress.org/trunk@36554 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/media.css

@@ -609,7 +609,7 @@ border color while dragging a file over the uploader drop area */
 }
 
 .media-frame.mode-grid .attachments-browser .no-media {
-	color: #999;
+	color: #666; /* same as no plugins and no themes */
 	font-size: 18px;
 	font-style: normal;
 	margin: 0;