web-server/doc/en/user/source/styling/sld/extensions/artifacts/shadow.sld

<StyledLayerDescriptor version="1.0.0" xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
  <NamedLayer>
    <Name>Default Polygon</Name>
    <UserStyle>
      <Title>Default polygon style</Title>
      <Abstract>A sample style that just draws out a solid gray interior with a black 1px outline</Abstract>
      <FeatureTypeStyle>
        <Rule>
          <Title>Shadow</Title>
          <PolygonSymbolizer>
            <Geometry>
               <ogc:Function name="offset">
                  <ogc:PropertyName>the_geom</ogc:PropertyName>
                  <ogc:Literal>0.00004</ogc:Literal>
                  <ogc:Literal>-0.00004</ogc:Literal>
               </ogc:Function>
            </Geometry>
            <Fill>
              <CssParameter name="fill">#555555</CssParameter>
            </Fill>
          </PolygonSymbolizer>
        </Rule>
      </FeatureTypeStyle>
      <FeatureTypeStyle>
        <Rule>
          <Title>Polygon</Title>
          <PolygonSymbolizer>
            <Fill>
              <CssParameter name="fill">#CCCCCC</CssParameter>
            </Fill>
            <Stroke>
              <CssParameter name="stroke">#000000</CssParameter>
              <CssParameter name="stroke-width">0.5</CssParameter>
            </Stroke>
          </PolygonSymbolizer>
        </Rule>
      </FeatureTypeStyle>

    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>