Index: wp-content/themes/twentyfifteen/style.css
===================================================================
--- wp-content/themes/twentyfifteen/style.css	(revision 30029)
+++ wp-content/themes/twentyfifteen/style.css	(working copy)
@@ -1178,7 +1178,55 @@
 	z-index: 100000;
 }
 
+a:focus,
+a:hover {
+	text-decoration: underline;
+}
 
+.entry-content a:focus,
+.entry-content a:hover,
+.social-navigation a:focus:before,
+.social-navigation a:hover:before,
+.comment-reply-title small a:focus:before,
+.comment-reply-title small a:hover:before,
+.comment-navigation .nav-next a:focus:after,
+.comment-navigation .nav-next a:hover:after,
+.comment-navigation .nav-previous a:focus:before,
+.comment-navigation .nav-previous a:hover:before,
+.posted-on a:focus:before,
+.posted-on a:hover:before,
+.byline a:focus:before,
+.byline a:hover:before,
+.cat-links span + a:focus:before,
+.cat-links span + a:hover:before,
+.tags-links span + a:focus:before,
+.tags-links span + a:hover:before,
+.comments-link a:focus:before,
+.comments-link a:hover:before,
+.entry-format a:focus:before,
+.entry-format a:hover:before,
+.edit-link a:focus:before,
+.edit-link a:hover:before,
+.full-size-link a:focus:before,
+.full-size-link a:hover:before,
+.pagination .prev:focus:before,
+.pagination .prev:focus:before,
+.pagination .next:focus:before,
+.pagination .next:hover:before,
+.image-navigation a:focus:before,
+.image-navigation a:hover:before,
+.image-navigation a:focus:after,
+.image-navigation a:hover:after,
+.format-link .entry-title a:focus:after,
+.format-link .entry-title a:hover:after,
+.entry-content .more-link:focus:after,
+.entry-content .more-link:hover:after,
+.author-link:focus:after,
+.author-link:hover:after {
+	text-decoration: none;
+	border-bottom: none;
+}
+
 /**
  * 8.0 Alignments
  */