@mixin optional-at-root($sel) {
  @at-root #{if(not &, $sel, selector-append(&, $sel))} {
    @content;
  }
}

@mixin placeholder-prefixer {
  @include optional-at-root('::-webkit-input-placeholder') { @content; }
  @include optional-at-root(':-moz-placeholder') { @content; }
  @include optional-at-root('::-moz-placeholder') { @content; }
  @include optional-at-root(':-ms-input-placeholder') { @content; }
}

@mixin placeholder($color: rgba(200, 200, 200, .8)) {
  @include placeholder-prefixer {
    color: $color;
    @content;
  }
}