Update default.html

_layouts/default.html

@@ -334,6 +334,23 @@ document.onmousedown = document.onmouseup = function(e) {
   }
 };
 </script>
+	<script>const btn = document.querySelector(".btn-toggle");
+
+const currentTheme = localStorage.getItem("theme");
+if (currentTheme == "dark") {
+  document.body.classList.add("dark-theme");
+}
+
+btn.addEventListener("click", function () {
+  document.body.classList.toggle("dark-theme");
+
+  let theme = "light";
+  if (document.body.classList.contains("dark-theme")) {
+    theme = "dark";
+  }
+  localStorage.setItem("theme", theme);
+});</script>
 <!---The Times 03/Jan/2009 Chancellor on brink of second bailout for banks--->
+	
 </body>
 </html>