scss-theming-5-themify.scss

@import 'themes.scss';

@mixin themify($themes: $themes) {
  @each $theme, $map in $themes {

    .theme-#{$theme} & {
      $theme-map: () !global;
      @each $key, $submap in $map {
        $value: map-get(map-get($themes, $theme), '#{$key}');
        $theme-map: map-merge($theme-map, ($key: $value)) !global;
      }

      @content;
      $theme-map: null !global;
    }

  }
}

scss-theming-6-themed.scss

@function themed($key) {
  @return map-get($theme-map, $key);
}

If this isn't working apply the className to body element.