How to see changes in django admin base.css

I want to change some css in static/admin/css/base.css

After some attempts I now fail to understand the static-file concept at all.
As a matter of fact I can delete the whole static directory without any effect/error (browser CTRL + F5).

# settings.py STATIC_URL = "static/" STATIC_ROOT = BASE_DIR.joinpath('static') # urls.py if settings.DEBUG: urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT) urlpatterns += static(settings.STATIC_URL, document_root=settings.STATIC_ROOT)

Long story short; How to change base.css?