reduced.mss

#country-label[zoom>1]{

  polygon-opacity:1;
  
  [zoom=1] { polygon-opacity: 0.5; }
  
  [zoom>=1][A = 1],
  [zoom>=2][A = 2],
  [zoom>=3][A = 3] { polygon-opacity: 0.1; }
  
  [zoom>=1][B = 1],
  [zoom>=2][B = 2],
  [zoom>=3][B = 3] { polygon-opacity: 0.2; }

}

reduced.xml

<Style name="layer" filter-mode="first" >
  <Rule>
  <!--2 -> 22-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <Filter>([A] = 3)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--2 -> 22-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <Filter>([B] = 1)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--2 -> 22-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <Filter>([B] = 2)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--3 -> 22-->
    <MaxScaleDenominator>100000000</MaxScaleDenominator>
    <Filter>([A] = 1)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--2 -> 2-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <MinScaleDenominator>100000000</MinScaleDenominator>
    <Filter>([A] = 1)</Filter>
    <PolygonSymbolizer fill-opacity="0.1" />
  </Rule>
  <Rule>
	<!--3 -> 22-->
    <MaxScaleDenominator>100000000</MaxScaleDenominator>
    <Filter>([A] = 2)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--2 -> 2-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <MinScaleDenominator>100000000</MinScaleDenominator>
    <Filter>([A] = 2)</Filter>
    <PolygonSymbolizer fill-opacity="0.1" />
  </Rule>
  <Rule>
	<!--3 -> 22-->
    <MaxScaleDenominator>100000000</MaxScaleDenominator>
    <Filter>([B] = 3)</Filter>
    <PolygonSymbolizer fill-opacity="0.2" />
  </Rule>
  <Rule>
	<!--2 -> 2-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <MinScaleDenominator>100000000</MinScaleDenominator>
    <Filter>([B] = 3)</Filter>
    <PolygonSymbolizer fill-opacity="1" />
  </Rule>
  <Rule>
	<!--2 -> 22-->
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <PolygonSymbolizer fill-opacity="1" />
  </Rule>
</Style>