diff --git a/public/theme-init.js b/public/theme-init.js
new file mode 100644
index 0000000..0924375
--- /dev/null
+++ b/public/theme-init.js
@@ -0,0 +1,21 @@
+// public/theme-init.js
+// Runs on every page and applies the saved theme *before* the page renders.
+
+(function () {
+  var STORAGE_KEY = "convertx-theme";
+
+  try {
+    var theme = localStorage.getItem(STORAGE_KEY);
+
+    // default to light if nothing stored or value is invalid
+    if (theme === "dark") {
+      document.documentElement.setAttribute("data-theme", "dark");
+    } else {
+      document.documentElement.removeAttribute("data-theme");
+    }
+  } catch (e) {
+    // If localStorage is blocked, just fall back to light theme
+    document.documentElement.removeAttribute("data-theme");
+  }
+})();
+