.button {
  & when (@theme = dark) {
    color: white;
  }
  & when not (@theme = variable) {
    border-color: red;
  }
  & when ( @x = 0.50 ) and ( iscolor( @c ) ) {
    background: blue;
  }
  width: 100%;
}
.rule when ( @mode = huge ) {
  width: 100%;
}
.mixin (@a) when (lightness(@a) >= 50%) {
  background-color: black;
}
.guarded(@color) when (@theme = dark) and not (@compat = ie9) {
  color: @color;
}
