code: function _replaceSelector(matchedSelector, val, selector) {
    return matchedSelector.replace(_replaceRegExp(val), (_, first, last) =>
      first + selector + last);
  }
docs: Private: replaces selector with inherit property inserted.
  
  * `matchedSelector` {String} selector of the rule that matches the inherit value
  * `val` {String} value of the inherit property
  * `selector` {String} selector of the rule that contains the inherit declaration.
  
  Returns {String} new selector.