**Steps to replicate the issue** (include links if applicable):
* Go to https://doc.wikimedia.org/oojs/master/ using either Firefox mobile or using Firefox devtools responsive design mode
* Click the menu button at the top of the screen
**What happens?**:
The menu is transparent, appears behind the page content, and clicking either "namespace" or "classes" does not produce any effect
**What should have happened instead?**:
The menu should appear above the page content, and should have an opaque background. Clicking either of the options should send the user to the relevant part of the site.
**Other information** (browser name/version, screenshots, etc.):
* Observed using Firefox mobile 103.2.0, and per conversation on IRC also when using Firefox devtools responsive design mode
Works as intended on Firefox desktop and Chrome mobile
{F35434975}