Generated by SassMeister.com.

SassMeister-input.scss

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

$themes: (
  theme1: theme-light,
  theme2: theme-dark
);

@function setStyle($map, $object, $style) {
  @if map-has-key($map, $object) {
    @return map-get(map-get($map, $object), $style);
  }
  @warn "The key ´#{$object} is not available in the map.";
  @return null;
}

$config: (
  theme1: (
    background: #f2f2f2,
    color: #000
  ),
  theme2: (
    background: #666,
    color: #fff
  )
);

.m-button {
  @each $key, $value in $themes {
    @if map-has-key($config, $key) {
      .#{$value} & {
        background: setStyle($config, $key, background);
        color: setStyle($config, $key, color);
      }
    } @else {
      @warn "The key ´#{$key} isn’t defined in the map $config´"
    }
  }
}

SassMeister-output.css

.theme-light .m-button {
  background: #f2f2f2;
  color: #000;
}

.theme-dark .m-button {
  background: #666;
  color: #fff;
}