diff --git a/packages/playground/src/index.html b/packages/playground/src/index.html
index 7ceafd1..aa0685a 100644
--- a/packages/playground/src/index.html
+++ b/packages/playground/src/index.html
@@ -1,6 +1,8 @@
+<!DOCTYPE html>
 <html>
   <head>
     <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Playground – Theatre.js</title>
     <style>
       body {
