diff --git a/EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/signflow-theme.js b/EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/signflow-theme.js
new file mode 100644
index 00000000..10af2992
--- /dev/null
+++ b/EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/signflow-theme.js
@@ -0,0 +1,46 @@
+/**
+ * signFLOW Theme Helper
+ * Called from ThemeService (Blazor WASM) to apply theme changes
+ * without relying on Blazor's HeadContent reactive updates.
+ */
+window.signflowTheme = {
+
+ /**
+ * Applies the DevExpress theme CSS by updating (or creating) the
+ * element in .
+ * Also sets data-bs-theme on for Bootstrap 5 dark mode.
+ *
+ * @param {string} href - full CSS href, e.g. "_content/DevExpress.Blazor.Themes/fluent.dark.bs5.min.css"
+ * @param {string} bsTheme - "dark" or "light"
+ */
+ apply: function (href, bsTheme) {
+ console.debug('[signflowTheme] apply', href, bsTheme);
+
+ // ── Bootstrap dark mode ─────────────────────────────────────────
+ document.documentElement.setAttribute('data-bs-theme', bsTheme);
+
+ // ── DevExpress theme CSS link ────────────────────────────────────
+ // Remove any other DevExpress theme links that were injected by SSR
+ // (HeadContent renders a on the server that stays in DOM).
+ document.querySelectorAll('link[href*="DevExpress.Blazor.Themes"]').forEach(function(el) {
+ if (el.id !== 'dx-theme-link') {
+ el.parentNode.removeChild(el);
+ }
+ });
+
+ let link = document.getElementById('dx-theme-link');
+
+ if (!link) {
+ link = document.createElement('link');
+ link.id = 'dx-theme-link';
+ link.rel = 'stylesheet';
+ document.head.appendChild(link);
+ }
+
+ // Compare using the relative path part only (link.href returns absolute URL)
+ const currentRelative = link.getAttribute('href') || '';
+ if (currentRelative !== href) {
+ link.setAttribute('href', href);
+ }
+ }
+};