diff --git a/packages/csr/src/reactive-runtime.ts b/packages/csr/src/reactive-runtime.ts
index a03622be..d92d4b12 100644
--- a/packages/csr/src/reactive-runtime.ts
+++ b/packages/csr/src/reactive-runtime.ts
@@ -221,6 +221,36 @@ export const REACTIVE_RUNTIME = String.raw`
       { binding: statement, functionName: match[1] },
     );
   }
+
+  function warnMissingThemeTokens() {
+    var referenced = Object.create(null);
+    function collect(rules) {
+      Array.prototype.forEach.call(rules || [], function (rule) {
+        var cssText = rule.cssText || "";
+        var match;
+        var pattern = /var\(\s*(--wire-[A-Za-z0-9_-]+)/g;
+        while ((match = pattern.exec(cssText))) referenced[match[1]] = true;
+        try {
+          if (rule.cssRules) collect(rule.cssRules);
+        } catch (_) {
+          // Cross-origin and disabled stylesheets can deny CSSOM access.
+        }
+      });
+    }
+    Array.prototype.forEach.call(document.styleSheets || [], function (sheet) {
+      try { collect(sheet.cssRules); } catch (_) {}
+    });
+    var rendered = window.getComputedStyle(document.documentElement);
+    Object.keys(referenced).forEach(function (token) {
+      if (rendered.getPropertyValue(token).trim()) return;
+      warnOnce(
+        "WRN-DEV-THEME-TOKEN-MISSING",
+        "Theme token '" + token + "' is referenced by rendered CSS but is not defined.",
+        document.documentElement,
+        { token: token },
+      );
+    });
+  }
   /*__WRNEXUS_DEV_END__*/
 
   function scheduleUpdateHook(element, callback) {
@@ -3438,6 +3468,9 @@ export const REACTIVE_RUNTIME = String.raw`
     hydratePreferenceControllers(host);
     hydrateSelectControllers(host);
     hydratePinInputControllers(host);
+    /*__WRNEXUS_DEV_START__*/
+    warnMissingThemeTokens();
+    /*__WRNEXUS_DEV_END__*/
   }
 
   var navbarOutsideClickBound = false;
diff --git a/packages/csr/test/reactive.test.ts b/packages/csr/test/reactive.test.ts
index c00855d5..81a4ed0d 100644
--- a/packages/csr/test/reactive.test.ts
+++ b/packages/csr/test/reactive.test.ts
@@ -724,6 +724,32 @@ test("development runtime warns when a component binding names a missing functio
   expect(String(warnings[0]?.[0])).toContain("missingSave");
 });
 
+test("development runtime warns for referenced theme tokens absent from rendered CSS", () => {
+  const win = new Window() as unknown as Window & Record<string, unknown>;
+  win.document.head.innerHTML =
+    `<style>:root { --wire-present-test: red; } .probe { ` +
+    `color: var(--wire-present-test); background: var(--wire-missing-test); }</style>`;
+  win.document.body.innerHTML = `<div class="probe" data-scope=""></div>`;
+  (globalThis as Record<string, unknown>).window = win;
+  (globalThis as Record<string, unknown>).document = win.document;
+  (globalThis as Record<string, unknown>).location = win.location;
+  (globalThis as Record<string, unknown>).NodeFilter = (win as unknown as { NodeFilter: unknown }).NodeFilter;
+  (globalThis as Record<string, unknown>).MutationObserver = (win as unknown as { MutationObserver: unknown }).MutationObserver;
+  (globalThis as Record<string, unknown>).CustomEvent = (win as unknown as { CustomEvent: unknown }).CustomEvent;
+  const warnings: unknown[][] = [];
+  const originalWarn = console.warn;
+  console.warn = (...args: unknown[]) => warnings.push(args);
+  try {
+    (0, eval)(getReactiveRuntime(true));
+    (win as unknown as { __wrnexusHydrateScopes?: (root: unknown) => void }).__wrnexusHydrateScopes?.(win.document);
+  } finally {
+    console.warn = originalWarn;
+  }
+  expect(warnings).toHaveLength(1);
+  expect(String(warnings[0]?.[0])).toContain("WRN-DEV-THEME-TOKEN-MISSING");
+  expect(String(warnings[0]?.[0])).toContain("--wire-missing-test");
+});
+
 test("production runtime strips development diagnostics", () => {
   const production = getReactiveRuntime();
   expect(production).not.toContain("WRN-DEV-");