Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

@mixin hover() {
  @if ($current_block != false) {
    #{$current_block}:hover & {
      @content;
    }
  }
  @else {
    @warn "Hover mixin called outside of a block";
  }
}

@mixin element($element) {
  $current_block: #{&} !global;
  &__#{$element} {
    @content;
  }
  // Step out of the current module.
  $current_block: false !global;
}

.story-box {
  @include element(header) {
    font-weight: 500;
    
    @include hover() {
      text-decoration: underline;
    }
  }
}

SassMeister-output.css

.story-box__header {
  font-weight: 500;
}

.story-box:hover .story-box__header {
  text-decoration: underline;
}