add 'custom_css' setting to model; check for 'custom_css' in template; create custom css dir in dockerfile

docker/Dockerfile.BackgroundJob

@@ -94,6 +94,8 @@ RUN apk add --no-cache mariadb-connector-c postgresql-client py3-gunicorn py3-ps
 COPY --from=builder /usr/bin/flask /usr/bin/
 COPY --from=builder /usr/lib/python3.8/site-packages /usr/lib/python3.8/site-packages/
 COPY --from=builder --chown=root:${USER} /app /app/
+# Create directory for custom css
+RUN mkdir /app/powerdnsadmin/static/custom 
 COPY ./docker/entrypoint.sh /usr/bin/
 
 WORKDIR /app

powerdnsadmin/models/setting.py

@@ -181,6 +181,7 @@ class Setting(db.Model):
         },
         'ttl_options': '1 minute,5 minutes,30 minutes,60 minutes,24 hours',
         'otp_field_enabled': True,
+        'custom_css': '',
     }
 
     def __init__(self, id=None, name=None, value=None):

powerdnsadmin/templates/login.html

@@ -11,7 +11,9 @@
   {% assets "css_login" -%}
   <link rel="stylesheet" href="{{ ASSET_URL }}">
   {%- endassets %}
-
+{% if SETTING.get('custom_css') %}
+  <link rel="stylesheet" href="/static/custom/{{ custom_css }}">
+{% endif %}
   <!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
   <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
   <!--[if lt IE 9]>