#world {
  polygon-fill: #000;
  [zoom=22] { polygon-fill: #f00000; }
  [zoom=21] { polygon-fill: #0f0000; }
  [zoom=20] { polygon-fill: #00f000; }
  [zoom=19] { polygon-fill: #000f00; }
  [zoom=18] { polygon-fill: #0000f0; }
  [zoom=17] { polygon-fill: #00000f; }
}