diff --git a/src/main.tsx b/src/main.tsx
index cd5e83d..71d69c2 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -10,6 +10,11 @@ import './styles/globals.css';
 import 'katex/dist/katex.min.css';
 import { initializeDefaultTransports } from './lib/api-client';
 
+const platform = window.electron?.platform;
+if (platform) {
+  document.documentElement.dataset.platform = platform;
+}
+
 initializeDefaultTransports();
 
 ReactDOM.createRoot(document.getElementById('root')!).render(
diff --git a/src/styles/globals.css b/src/styles/globals.css
index 622925d..1da7010 100644
--- a/src/styles/globals.css
+++ b/src/styles/globals.css
@@ -219,6 +219,48 @@
   backdrop-filter: blur(18px) saturate(135%);
 }
 
+/* Chromium's backdrop sampling is disproportionately expensive for transient
+ * layers in macOS Electron windows. Keep the optimization platform-scoped so
+ * the shared materials remain unchanged elsewhere. */
+html[data-platform='darwin'] :is(
+  [role='dialog'],
+  [role='alertdialog'],
+  [role='menu'],
+  [role='listbox'],
+  [role='tooltip'],
+  .fixed.inset-0
+),
+html[data-platform='darwin'] :is(
+  [role='dialog'],
+  [role='alertdialog'],
+  [role='menu'],
+  [role='listbox'],
+  [role='tooltip'],
+  .fixed.inset-0
+) .glass-surface {
+  -webkit-backdrop-filter: none !important;
+  backdrop-filter: none !important;
+}
+
+html[data-platform='darwin'] :is(
+  [role='dialog'],
+  [role='alertdialog'],
+  [role='menu'],
+  [role='listbox'],
+  [role='tooltip'],
+  .fixed.inset-0
+).glass-surface,
+html[data-platform='darwin'] :is(
+  [role='dialog'],
+  [role='alertdialog'],
+  [role='menu'],
+  [role='listbox'],
+  [role='tooltip'],
+  .fixed.inset-0
+) .glass-surface {
+  background-color: hsl(var(--background));
+}
+
 /* Sidebar material: keep the rail visibly white while allowing a restrained
  * amount of the canvas to show through. A low white alpha reads as gray over
  * the transparent native window material, so the light surface needs to stay
diff --git a/tests/e2e/popup-performance.spec.ts b/tests/e2e/popup-performance.spec.ts
new file mode 100644
index 0000000..494c5cf
--- /dev/null
+++ b/tests/e2e/popup-performance.spec.ts
@@ -0,0 +1,62 @@
+import { expect, getStableWindow, test } from './fixtures/electron';
+
+type PopupStyles = {
+  contentBackdropFilter: string;
+  overlayBackdropFilter: string;
+};
+
+async function readPopupStyles(page: Awaited<ReturnType<typeof getStableWindow>>): Promise<PopupStyles> {
+  return await page.evaluate(() => {
+    const content = document.querySelector<HTMLElement>('[role="dialog"]');
+    const overlay = [...document.querySelectorAll<HTMLElement>('.fixed.inset-0')]
+      .find((element) => element.getAttribute('role') !== 'dialog');
+    if (!overlay || !content) {
+      throw new Error('Expected the open dialog overlay and content');
+    }
+
+    const contentStyle = getComputedStyle(content);
+    const overlayStyle = getComputedStyle(overlay);
+    return {
+      contentBackdropFilter: contentStyle.backdropFilter,
+      overlayBackdropFilter: overlayStyle.backdropFilter,
+    };
+  });
+}
+
+test.describe('shared popup rendering cost', () => {
+  test('disables transient popup backdrop filters only on macOS', async ({ launchElectronApp }) => {
+    const app = await launchElectronApp({ skipSetup: true });
+
+    try {
+      const page = await getStableWindow(app);
+      const actualPlatform = await page.evaluate(() => window.electron.platform);
+      await expect(page.locator('html')).toHaveAttribute('data-platform', actualPlatform);
+
+      await expect(page.getByTestId('ai-module-selection-page')).toBeVisible();
+      await page.getByTestId('ai-module-option-programming').click();
+      await expect(page.getByTestId('main-layout')).toBeVisible();
+      await page.getByTestId('sidebar-member-menu-trigger').click();
+      await page.getByTestId('sidebar-nav-settings').click();
+      await expect(page.getByTestId('settings-page')).toBeVisible();
+      await page.getByTestId('settings-reveal-additional').click();
+      await expect(page.getByRole('dialog')).toBeVisible();
+
+      await page.evaluate(() => {
+        document.documentElement.dataset.platform = 'darwin';
+      });
+      await expect.poll(() => readPopupStyles(page)).toEqual({
+        contentBackdropFilter: 'none',
+        overlayBackdropFilter: 'none',
+      });
+
+      await page.evaluate(() => {
+        document.documentElement.dataset.platform = 'win32';
+      });
+      const nonMacStyles = await readPopupStyles(page);
+      expect(nonMacStyles.contentBackdropFilter).not.toBe('none');
+      expect(nonMacStyles.overlayBackdropFilter).not.toBe('none');
+    } finally {
+      await app.evaluate(({ app: electronApp }) => electronApp.quit());
+    }
+  });
+});