Fix some hints.

lib/src/ast/selector/pseudo.dart

@@ -50,6 +50,7 @@ class PseudoSelector extends SimpleSelector {
 
       result.add(simple);
     }
+    if (!addedThis) result.add(this);
 
     return result;
   }

lib/src/ast/selector/universal.dart

@@ -3,7 +3,6 @@
 // https://opensource.org/licenses/MIT.
 
 import '../../extend/functions.dart';
-import '../../utils.dart';
 import '../selector.dart';
 
 class UniversalSelector extends SimpleSelector {

lib/src/extend/extender.dart

@@ -9,7 +9,6 @@ import 'package:collection/collection.dart';
 import 'package:source_span/source_span.dart';
 
 import '../ast/css/node.dart';
-import '../ast/sass/expression.dart';
 import '../ast/selector.dart';
 import '../utils.dart';
 import 'functions.dart';
@@ -28,7 +27,7 @@ class Extender {
   CssStyleRule addSelector(CssValue<SelectorList> selectorValue,
       {FileSpan span}) {
     var selector = selectorValue.value;
-    for (var complex in selector.value.components) {
+    for (var complex in selector.components) {
       for (var component in complex.components) {
         if (component is CompoundSelector) {
           for (var simple in component.components) {

lib/src/utils.dart

@@ -10,7 +10,6 @@ import 'package:collection/collection.dart';
 import 'package:source_span/source_span.dart';
 
 import 'ast/node.dart';
-import 'ast/selector.dart';
 import 'value/number.dart';
 
 const _epsilon = 1 / (10 * SassNumber.precision);

lib/src/visitor/css/serialize.dart

@@ -8,7 +8,6 @@ import '../../ast/css/node.dart';
 import '../../util/character.dart';
 import '../../value.dart';
 import '../css.dart';
-import '../../parser.dart';
 
 String toCss(CssNode node) {
   var visitor = new _SerializeCssVisitor();