Steps to reproduce:

1. Open any diff page on the mobile site, e.g.: https://en.wikipedia.org/w/index.php?title=Main_Page&diff=prev&oldid=1319805659&useskin=minervanue
2. Enable Dark Mode in settings.
3. On desktop, open DevTools → responsive mode and set the width below 640px (or select any mobile preset) to simulate the mobile layout.

Observed behavior:
When scrolling to the bottom of the page, the site logo watermark appears in white and overlays all content.
Example clip:

Expected behavior:
In Dark Mode, the logo should stay hidden, the same way it is hidden in Light Mode.