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 +1178,19 @@
 	z-index: 100000;
 }
 
+a:focus,
+a:hover {
+	text-decoration: underline;
+}
 
+.entry-content a:focus,
+.entry-content a:hover,
+.entry-footer a:focus:before,
+.entry-footer a:hover:before {
+	text-decoration: none;
+	border-bottom: none;
+}
+
 /**
  * 8.0 Alignments
  */