anchor.diff:    }
   
     Value visitSelectorExpression(SelectorExpression node) {
  -    if (_selector == null) return sassNull;
  -    return _selector.value.asSassList;
  +    var selector = _selector ?? _selectorOutsideAtRoot;
  +    if (selector == null) return sassNull;
  +    return selector.value.asSassList;
     }
   
     SassString visitStringExpression(StringExpression node) =>
  
positive.code:       _environment.scope(callback);
        _parent = oldParent;
      };
  
      if (query.excludesMedia) {
        var innerScope = scope;
  
negative.code:   /// The current selector, if any.
    CssValue<SelectorList> _selector;
  
    /// The value of [_selector] outside an `@at-root` statement that excludes
    /// style rules.
    ///
    /// This is separate from [_selector] because `&` can see it but parent
    /// resolution cannot.
    CssValue<SelectorList> _selectorOutsideAtRoot;
  
    /// The current media queries, if any.
    List<CssMediaQuery> _mediaQueries;
  
  