In the last section after applying the login functionality, I noticed there is a mistake in light / dark mode switch. In the else statement, request.session['is_dark_mode'] should be set to True (not False). We will fix this together later, but I'm dropping here the correct code:

def change_theme(request):
    if 'is_dark_mode' in request.session:
        request.session['is_dark_mode'] = not request.session['is_dark_mode']
    else:
        request.session['is_dark_mode'] = True
    return HttpResponseRedirect(request.META.get('HTTP_REFERER'))