Does anyone know how to make OSM national_park style using GeoServer GeoCSS?

Question

Does anyone know how to make OSM national_park style using GeoServer's GeoCSS?
At the moment I've succeeded only using stroke-geometry: [buffer(geom, -10)], [geom];. But the result is not satisfying.
This is OSM National Park boundary style (below).

This is my style (below).

As you can see, when I zoom in, distance between original and buffered geometry increases.
Is there any better way? How to make that OSM style in proper way?

Dror Bogin · Accepted Answer

Assuming you want just the tiny one sided buffer you were very close,
what you were missing was the difference function:
fill-geometry: [difference(geom,buffer(geom, -200))];

This should work for you, with the distance you want.
Ian suggested you use pixels but i don't think the buffer will accept them as units,
so using multiple styles for different zoom levels is probably the best option.
##EDIT##
I tested a new style with @geowolf's answer and using a complete version to match most of the national park's style should look something like this:
* {
stroke: #00b200;
fill-opacity: 0;
stroke-opacity: 1, 0.3;
stroke-offset: 0,-5;
stroke-width: 1, 7;  }

Apart from the color which can be tinkered with, this pretty much does the job while using two symbolizers for the same line, and allows you to create the inner buffer with pixels instead of map units.

DPSSpatial · Answer

For reference, the style in the map you're after is found in a Mapnik Style file, located here:
https://github.com/gravitystorm/openstreetmap-carto
It might be worth trying to spin up Mapbox Studio, importing the data, applying that style, and engineering it from there.
Are you serving this up as a basemap from Geoserver, or as a dynamic layer?

Andrea Aime · Answer

Try using stroke-offset, that can be sized in pixels, e.g.:
  stroke: gray, green;
  stroke-offset: 0, 2;
  stroke-width: 1, 2;

Does anyone know how to make OSM national_park style using GeoServer GeoCSS?

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