diff --git a/apps/readest-app/src/__tests__/components/BookDetailView.test.tsx b/apps/readest-app/src/__tests__/components/BookDetailView.test.tsx
new file mode 100644
index 00000000..da19e583
--- /dev/null
+++ b/apps/readest-app/src/__tests__/components/BookDetailView.test.tsx
@@ -0,0 +1,102 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { render, cleanup, fireEvent } from '@testing-library/react';
+
+import { Book } from '@/types/book';
+import BookDetailView from '@/components/metadata/BookDetailView';
+import { DropdownProvider } from '@/context/DropdownContext';
+
+vi.mock('@/hooks/useTranslation', () => ({
+  useTranslation: () => (s: string) => s,
+}));
+
+vi.mock('@/store/settingsStore', () => ({
+  useSettingsStore: () => ({
+    settings: {
+      metadataSeriesCollapsed: true,
+      metadataOthersCollapsed: true,
+      metadataDescriptionCollapsed: true,
+    },
+  }),
+}));
+
+vi.mock('@/context/EnvContext', () => ({
+  useEnv: () => ({ envConfig: {}, appService: null }),
+}));
+
+vi.mock('@/helpers/settings', () => ({
+  saveSysSettings: vi.fn(),
+}));
+
+vi.mock('@/components/BookCover', () => ({
+  __esModule: true,
+  default: () => null,
+}));
+
+vi.mock('@/hooks/useResponsiveSize', () => ({
+  useResponsiveSize: (n: number) => n,
+  useDefaultIconSize: () => 20,
+}));
+
+vi.mock('next/image', () => ({
+  __esModule: true,
+  default: (props: Record<string, unknown>) => {
+    // biome-ignore lint/a11y/useAltText: test mock
+    return <img {...props} />;
+  },
+}));
+
+afterEach(() => cleanup());
+
+const makeBook = (overrides?: Partial<Book>): Book =>
+  ({
+    hash: 'abc123',
+    title: 'Test Book',
+    author: 'Test Author',
+    format: 'EPUB',
+    coverImageUrl: 'https://example.com/cover.jpg',
+    createdAt: Date.now(),
+    updatedAt: Date.now(),
+    downloadedAt: Date.now(),
+    uploadedAt: Date.now(),
+    ...overrides,
+  }) as Book;
+
+const renderView = (extra?: Partial<React.ComponentProps<typeof BookDetailView>>) =>
+  render(
+    <DropdownProvider>
+      <BookDetailView
+        book={makeBook()}
+        metadata={null}
+        fileSize={1024}
+        onDelete={vi.fn()}
+        onDeleteCloudBackup={vi.fn()}
+        onDeleteLocalCopy={vi.fn()}
+        {...extra}
+      />
+    </DropdownProvider>,
+  );
+
+describe('BookDetailView delete dropdown layout', () => {
+  it('places dropdown-center on the parent dropdown so the menu stays in flow', () => {
+    const { container } = renderView();
+    const toggle = container.querySelector('button[aria-label="Delete Book Options"]');
+    expect(toggle).toBeTruthy();
+    fireEvent.click(toggle!);
+
+    // The parent <details> should center its absolutely positioned content.
+    const details = container.querySelector('details.dropdown');
+    expect(details).toBeTruthy();
+    expect(details!.className).toContain('dropdown-center');
+
+    // The inner menu must NOT carry dropdown-center (which would force
+    // position: absolute on it and detach the menu from its anchor — the bug
+    // reported in https://github.com/readest/readest/issues/3940 where the
+    // menu shifted to the right when items were clicked).
+    const menu = container.querySelector('.delete-menu');
+    expect(menu).toBeTruthy();
+    expect(menu!.className).not.toContain('dropdown-center');
+    // It should keep position: relative via the !relative override so it
+    // anchors against the centered parent.
+    expect(menu!.className).toContain('!relative');
+  });
+});
diff --git a/apps/readest-app/src/components/metadata/BookDetailView.tsx b/apps/readest-app/src/components/metadata/BookDetailView.tsx
index 5f3176b4..e26c9cab 100644
--- a/apps/readest-app/src/components/metadata/BookDetailView.tsx
+++ b/apps/readest-app/src/components/metadata/BookDetailView.tsx
@@ -101,13 +101,13 @@ const BookDetailView: React.FC<BookDetailViewProps> = ({
             {onDelete && (
               <Dropdown
                 label={_('Delete Book Options')}
-                className='dropdown-bottom flex justify-center'
+                className='dropdown-bottom dropdown-center flex justify-center'
                 buttonClassName='btn btn-ghost h-8 min-h-8 w-8 p-0'
                 toggleButton={<MdOutlineDelete className='fill-red-500' />}
               >
                 <div
                   className={clsx(
-                    'delete-menu dropdown-content dropdown-center no-triangle',
+                    'delete-menu dropdown-content no-triangle !relative',
                     'border-base-300 !bg-base-200 z-20 mt-1 max-w-[90vw] shadow-2xl',
                   )}
                 >