I styled Geoserver maps with SLD. And now I have to convert this style to CSS. CSS is easier to support. Well, I have this fragment of SLD:

<Geometry>
    <ogc:Function name="offset">
        <ogc:PropertyName>way</ogc:PropertyName>
        <ogc:Literal>-13</ogc:Literal>
        <ogc:Literal>13</ogc:Literal>
    </ogc:Function>
</Geometry>

I don't know how to use 'offset' function in CSS. Can you help me?