anchor.diff:  body {
   color: @color1;
   }''';
  -      StyleSheet sheet = compile(css, polyfill: true);
  -
  -      expect(printStyleSheet(sheet, pretty: false), 'body { color: red; }');
  -    });
  +
  +      final generated = 'body { color: red; }';
  +      final generatedPretty = '''
  +body {
  +  color: #f00;
  +}''';
  +      checkPolyfill(css, generated); // the color is 'red'
  +      checkPrettyPolyfill(css, generatedPretty); // the color is '#f00';
  +    });
  +
       test('simple_less_rule', () {
         // not working
         String css = '''
  
positive.code:     });
  
      test('simple_css3_var_no_polyfill', () {
        String css = '''
  :host {
    --test-color1: red;
  }
  body {
    color: var(--test-color1);
  }''';
        StyleSheet sheet = compile(css);
  
        expect(printStyleSheet(sheet, pretty: false),
            ':host { --test-color1: red; } body { color: var(--test-color1); }');
      });
  
      test('simple_css3', () {
        // css3 vars not working
        String css = '''
  :host {
    --test-color1: red;
  }
  body {
    color: var(--test-color1);
  }''';
        StyleSheet sheet = compile(css,
            options: new PreprocessorOptions(polyfill: true), polyfill: true);
  
        expect(printStyleSheet(sheet, pretty: false),
            ':host { --test-color1: red; } body { color: ; }');
      });
  
      test('nested_rule', () {
  
negative.code: import 'package:csslib/parser.dart';
  import 'package:csslib/visitor.dart';
  import 'package:yacht/src/csslib_utils.dart';
  
  const simpleOptionsWithCheckedAndWarningsAsErrors = const PreprocessorOptions(
      useColors: false,
      checked: true,
      warningsAsErrors: true,
      inputFile: 'memory');
  
  checkCompile(String input, String generated,
      {bool pretty: false, bool polyfill: false}) {
    expect(compileCss(input, pretty: pretty, polyfill: polyfill), generated);
  }
  
  checkNoPolyfill(String input, String generated, {bool pretty: false}) =>
      checkCompile(input, generated, pretty: pretty, polyfill: false);
  checkPolyfill(String input, String generated, {bool pretty: false}) =>
      checkCompile(input, generated, pretty: pretty, polyfill: true);
  
  checkPrettyPolyfill(String input, String generated) =>
      checkPolyfill(input, generated, pretty: true);
  
  main() {
    group('csslib_utils', () {
  