diff -r 39d36c2db68e -r 7160bdd56b84 mercurial/templates/static/style-paper.css
--- a/mercurial/templates/static/style-paper.css	Sat Apr 08 14:33:20 2017 -0700
+++ b/mercurial/templates/static/style-paper.css	Thu Apr 06 19:15:09 2017 +0200
@@ -320,6 +320,22 @@
   font-family: sans-serif;
 }
 
+div#followlines-tooltip {
+  display: none;
+  position: fixed;
+  background-color: #ffc;
+  border: 1px solid #999;
+  padding: 2px;
+}
+
+.sourcelines:hover > div#followlines-tooltip {
+  display: inline;
+}
+
+.sourcelines:hover > div#followlines-tooltip.hidden {
+  display: none;
+}
+
 .sourcelines > a {
     display: inline-block;
     position: absolute;