SASS mixin for appending a selector to the parent of the current rule set.

sass-prepend-selector.scss

/// Nested [mixin]
/// --------------
/// Prepend a css rule to the current rule set.
/// @content         : <content>
/// @param $selector : <span>
/// @param $isParent : <span> Whether the $selector will be applied as a parent or not.

@mixin prepend-selector($selector, $isParent: true) {
  @if($isParent) {
    @at-root #{$selector} & {
      @content;
    }
  } @else {
    @at-root #{$selector}#{&} {
      @content;
    }
  }
}