diff --git a/handlers/form.html b/handlers/form.html
index edf915d..b853128 100644
--- a/handlers/form.html
+++ b/handlers/form.html
@@ -7,7 +7,11 @@
     <title>ladder</title>
     <script>
       const handleThemeChange = () => {
-        const theme = localStorage.getItem("theme");
+        let theme = localStorage.getItem("theme");
+        if (theme === null) {
+          localStorage.setItem("theme", "system");
+          theme = "system";
+        }
         if (
           theme === "dark" ||
           (theme === "system" &&