@mixin vw-font-size($viewport-width, $font-size, $letter-spacing: null) {

  $vw-context: $viewport-width * 0.01;

  @media (max-width: ($viewport-width * 1px)) {
    font-size: (($font-size / $vw-context) * 1vw);

    @if ($letter-spacing) {
      letter-spacing: (($letter-spacing / $vw-context) * 1vw);
    }

  }
}

@mixin vw-font-normalize($viewport-width, $font-size) {
  @media (max-width: ($viewport-width * 1px)) {
    font-size: ($font-size * 1px);
  }
}