I installed mailman3 on Debian Bookworm.  Version information:
* mailman 3.3.8-1 (including mailman3-full and mailman3-web 20200530-2.1)
* python3-django-mailman3 : 1.3.9-1
* python3-mailman-hyperkitty : 1.2.1

When I entered the Django admin page (/mailman3/admin/) , the first level
(landing page, showing all the administrative items like Mail domains, Failed
tasks, Favorites, ... etc.) is okay.  But when I clicked any of these item and
entered into the second level, the page was broken.  A first-level page covered
on top of it and I couldn't see the second level pages and hence could not
operate on it.

The screenshots can be found here:

https://nextcloud.slat.org/index.php/s/e5KKEEbqDK6DpiN
https://nextcloud.slat.org/index.php/s/nLgMRQ9ACyxCwoc

Such problems does not happen in mailman3 on Bullseye, which the version
information is
* mailman3-full 3.3.3-1
* python3-django-mailman3  1.3.5-2
* python3-mailman-hyperkitty 1.1.0-10

PS: system information is wrong since I'm reporting it on my own laptop, which
is Debian testing.  It happens on the mailman3 suite on Debian testing as well,
though.

I can confirm this bug. The admin interface is unusable, so it's not
possible to change or add a new site, which in turn renders the whole
installation unusable.

Please fix, thanks!