bem.scss

// https://css-tricks.com/bem-101/

=e($elements...)
  $selector: ()
  @each $element in $elements
    $selector: append($selector, unquote("&__" + $element), comma)
  #{$selector}
    @content
=m($modifiers...)
  $selector: ()
  @each $modifier in $modifiers
    $selector: append($selector, unquote("&--" + $modifier), comma)
  #{$selector}
    @content
    
.block {
  +e(child) {
    background: teal;
    +m(featured, important) {
      background: crimson;
    }
  }
}