Skin dropdown is expanded when clicking Customize

Steps to reproduce:

1. Log in to XWiki as an administrator.
2. Navigate to Administration > Look & Feel > Themes
3. Locate the Skin section.
4. Click the Customize button.
5. Observe that the Skin dropdown automatically expands.
6. Wait a few seconds and observe that it collapses automatically.

Actual result

The Skin dropdown is expanded when clicking Customize and remains open for a few seconds before collapsing on its own.

Expected result

The Skin dropdown should remain collapsed when clicking Customize. It should only expand when explicitly requested by the user.