gistfile1.txt

admin query for layer: 

( SELECT way, admin_level
  FROM planet_osm_line
  WHERE boundary = 'administrative'
) AS data

style in base.mss: 


#admin[admin_level=8][zoom>1] {
  line-color:@admin_2;
  line-width:4.5;
  [zoom=2] { line-opacity: 0.25; }
  [zoom=3] { line-opacity: 0.3; }
  [zoom=4] { line-opacity: 0.4; }
}