Country-specific masking in CartoCSS

mask.mss

Map {
  /*background-color: #b8dee6;*/
}

#countries[ADMIN='Nicaragua'] {
  polygon-fill:#abd69b;
  line-color:#754098;
  polygon-opacity:0;
  line-width:6;
  line-opacity:0.8;
  line-comp-op:hard-light;
  line-join:round;
}

#mask {
  ::mask {
    polygon-fill:#d7cebf;
    comp-op:dst-out;
    image-filters:agg-stack-blur(100,100);
  }
  ::shape {
    line-color:#754098;
    line-width:3;
    line-offset:3;
    line-join:round;
    line-opacity:0.7;
    line-comp-op:hard-light;
    image-filters: agg-stack-blur(1,1);
  }
}