That’s something I’ve never bothered with.
We adhere strictly to the principle stated in the docs at The Django admin site | Django documentation | Django
The admin’s recommended use is limited to an organization’s internal management tool. It’s not intended for building your entire front end around.
We consider the admin tool to be just that - a tool. It’s not our site’s front-end from any perspective and only used by an extremely limited number of people (2). Therefore, we don’t expend any effort to style that site - it is what it is.