foo {
  c0: opacity(rgba(0,0,0,0.0));
  c1: opacity(rgba(0,0,0,0.1));
  c2: opacity(rgba(0,0,0,0.2));
  c3: opacity(rgba(0,0,0,0.3));
  c4: opacity(rgba(0,0,0,0.4));
  c5: opacity(rgba(0,0,0,0.5));
  c6: opacity(rgba(0,0,0,0.6));
  c7: opacity(rgba(0,0,0,0.7));
  c8: opacity(rgba(0,0,0,0.8));
  c9: opacity(rgba(0,0,0,0.9));
  c10: opacity(rgba(0,0,0,1));
}