Index: wp-admin/themes.php
===================================================================
--- wp-admin/themes.php	(revision 32302)
+++ wp-admin/themes.php	(working copy)
@@ -363,7 +363,7 @@
 		<div class="theme-header">
 			<button class="left dashicons dashicons-no"><span class="screen-reader-text"><?php _e( 'Show previous theme' ); ?></span></button>
 			<button class="right dashicons dashicons-no"><span class="screen-reader-text"><?php _e( 'Show next theme' ); ?></span></button>
-			<button class="close dashicons dashicons-no"><span class="screen-reader-text"><?php _e( 'Close overlay' ); ?></span></button>
+			<button class="close dashicons dashicons-no"><span class="screen-reader-text"><?php _e( 'Close details dialog' ); ?></span></button>
 		</div>
 		<div class="theme-about">
 			<div class="theme-screenshots">