diff --git a/chapter1/99energy.html b/chapter1/99energy.html
index f3d24c0..985e29c 100644
--- a/chapter1/99energy.html
+++ b/chapter1/99energy.html
@@ -3,6 +3,7 @@
 <head>
 <title>My First JavaScript</title>
 <meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
 </head>
 <body>
 <script>
