diff --git a/effective-shell-playground/websites/simple/code.js b/effective-shell-playground/websites/simple/code.js
index 2d557084..165aac6d 100644
--- a/effective-shell-playground/websites/simple/code.js
+++ b/effective-shell-playground/websites/simple/code.js
@@ -1,10 +1,10 @@
 //  This function changes the header text for the webpage.
 function changeHeader(newHeader) {
-  document.getElementById("header").innerText = newHeader;
+  document.getElementById('header').innerText = newHeader;
 }
 
 //  When the webpage is loaded...
 window.addEventListener('DOMContentLoaded', function() {
   //  ...hide the warning message.
-  document.getElementById("warning").display = 'none';
+  document.getElementById('warning').style.display = 'none';
 });