anchor.diff:  
     void visitStyleRule(StyleRule node) {
       var selectorText = _performInterpolation(node.selector, trim: true);
  -    if (_styleRules.isNotEmpty) {
  +    if (_styleRule != null) {
         // TODO: semantically resolve parent references.
         selectorText = new CssValue(
  -          "${_styleRules.last.selector.value} ${selectorText.value}",
  +          "${_styleRule.selector.value} ${selectorText.value}",
             span: node.selector.span);
       }
   
  
positive.code:   final Environment _environment;
    final PerformExpressionVisitor _expressionVisitor;
  
    /// Style rules containing the currently visited node, from outermost to
    /// innermost.
    var _styleRules = <CssStyleRule>[];
  
    /// The children of the root stylesheet node.
    ///
  
negative.code:     // rule before any of its children.
      var insertionPoint = _outerChildren.isEmpty ? null : _outerChildren.last;
  
      var children = _withStyleRule(
          new CssStyleRule(selector, [], span: node.span),
          () => _collectChildren(() => super.visitStyleRule(node)));
      if (children.isEmpty) return;
  
      var rule = new CssStyleRule(selector, children, span: node.span);
  