How to hide and show layers with CartoCSS based on zoom

styleCities.css

/** cities style */

#populated_places{
  marker-fill-opacity: 0.8;
  marker-line-color: #FFF;
  marker-line-width: 0.2;
  marker-line-opacity: 0.7;
  marker-placement: point;
  marker-type: ellipse;
  marker-width: 10;
  marker-fill: #F11810;
  marker-allow-overlap: true;
  [zoom <= 5] {marker-opacity: 0}
}

styleCountries.css

/** countries style */

#world_borders{
  polygon-fill: #FFFFB2;
  polygon-opacity: 0.8;
  line-color: #FFF;
  line-width: 0.5;
  line-opacity: 1;
}
#world_borders [ pop_norm <= 247992435.530086] {
   polygon-fill: #B10026;
}
#world_borders [ pop_norm <= 4086677.23673585] {
   polygon-fill: #E31A1C;
}
#world_borders [ pop_norm <= 1538732.3943662] {
   polygon-fill: #FC4E2A;
}
#world_borders [ pop_norm <= 923491.374542489] {
   polygon-fill: #FD8D3C;
}
#world_borders [ pop_norm <= 616975.331234902] {
   polygon-fill: #FEB24C;
}
#world_borders [ pop_norm <= 326396.192958792] {
   polygon-fill: #FED976;
}
#world_borders [ pop_norm <= 95044.5589361554] {
   polygon-fill: #FFFFB2;
}
#world_borders [zoom > 5] {polygon-opacity: 0}