@if $use-selection == true {
  //------------------------------------
  //  SELECTION
  //------------------------------------
  * {
    &::-webkit-selection {
      background-color: $selection-background;
      color: $selection-color;
    }

    &::-moz-selection {
      background-color: $selection-background;
      color: $selection-color;
    }

    &::selection {
      background-color: $selection-background;
      color: $selection-color;
    }
  }
}

@if $use-selection == true {
  //------------------------------------
  //  SELECTION
  //------------------------------------

  // Silent Class
  %selection-style {
    background-color: $selection-background;
    color: $selection-color;
  }


  // Selection Style
  * {
    &::-webkit-selection {
      @extend %selection-style;
    }

    &::-moz-selection {
      @extend %selection-style;
    }

    &::selection {
      @extend %selection-style;
    }
  }
}

Create a silent classes that contains selection styles
Create a silent classes that contains selection styles
