diff --git a/static/demos/light-dark-demo-4/sw.js b/static/demos/light-dark-demo-4/sw.js
index 3149d59..a08543b 100644
--- a/static/demos/light-dark-demo-4/sw.js
+++ b/static/demos/light-dark-demo-4/sw.js
@@ -3,7 +3,7 @@ self.addEventListener("fetch", event =>{
     event.respondWith((async ()=>{
         const resp = await fetch(event.request);
         const body = await resp.text();
-        new Response(body.replace("<body>", '<body class="toggled">'), {
+        return new Response(body.replace("<body>", '<body class="toggled">'), {
             ...resp
         });
     })());
