Django admin showing a white box instead of toggle theme icon

As I open Django admin page, a wide white box appears instead of the theme icon (using Django 4.2.1).

While testing on Docker container, everything seems ok.

I have been looking at the documentation on overriding admin/base.html, but I'm not sure this is the issue.

Checking the log after deployment (on EC cloud), nothing comes to my attention.

I am letting serve the static content by nginx (1.23).

python manage.py collectstatic --noinput

Overall, all static files are working properly on the rest of the site.

I tried inspecting the element <button class="theme-toggle">. Nothing anomalous.

Everything looks normal to me. Apart from this, production looks identical to the Docker container.