$theme:(
   theme1: (width: 10px),
   theme2: (width: 20px)
)

@include loopTheme($theme) {
   <!-- ***** below code DOEST NOT work *****-->
   width: calc(#{map-get($theme, "width")} + 1px);

   <!-- this approach works -->
   width: map-get($theme, "width")

}


@mixin loopTheme($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;
    }
  }
}