Drop shadows in Carto

gistfile1.txt

#countries {
  ::shadow1, ::shadow2, ::shadow3 {
    line-color: #024;
    line-join: round;
  }
  ::shadow1 {
    line-opacity: 0.03;
    line-width: 7;
  }
  ::shadow2 {
    line-opacity: 0.06;
    line-width: 5;
  }
  ::shadow3 {
    line-opacity: 0.12;
    line-width: 3;
  }
  polygon-fill: #fff;
}