function parseDropShadow(shadow) {
    var newShadow;

    if (shadow.length === 3) { // [h-shadow, v-shadow, color]
      newShadow = [shadow[0], shadow[1], 0, shadow[2]];
    } else if (shadow.length === 4) { // ideal [<offset-x>, <offset-y>, <blur-radius>, <color>]
      newShadow = [shadow[0], shadow[1], shadow[2], shadow[3]];
    }

    // make sure the values are ready to tween
    for (var i = 0; i < 3; i += 1) {
      newShadow[i] = parseFloat(newShadow[i]);
    }
    // also the color must be a rgb object
    newShadow[3] = trueColor(newShadow[3]);
    return newShadow;
  }
Returns `drop-shadow` sub-property object.
@param {(string | number)[]} shadow and `Array` with `drop-shadow` parameters
@returns {KUTE.filterList['dropShadow']} the expected `drop-shadow` values