[css_colors] Adopt code excerpts in README (#5478)

Updates the README to use a compiled excerpt source for its example of importing and using `CSSColors`.

Part of [flutter/flutter#102679](https://github.com/flutter/flutter/issues/102679)

packages/css_colors/CHANGELOG.md

@@ -1,6 +1,7 @@
-## NEXT
+## 1.1.4
 
 * Updates minimum supported SDK version to Flutter 3.10/Dart 3.0.
+* Improves README example and updates it to use code excerpts.
 
 ## 1.1.3
 

packages/css_colors/README.md

@@ -5,16 +5,10 @@ This package defines color constants for the CSS colors. These color constants
 use the [Color](https://api.flutter.dev/flutter/dart-ui/Color-class.html) class
 from `dart:ui`, which means they're useful for Flutter apps.
 
-Import
-------
-
-```dart
-import 'package:css_colors/css_colors.dart';
-```
-
 Use
 ---
 
+<?code-excerpt "test/css_colors_test.dart (Usage)"?>
 ```dart
-new Container(color: CSSColors.orange)
+final Container orange = Container(color: CSSColors.orange);
 ```

packages/css_colors/pubspec.yaml

@@ -2,7 +2,7 @@ name: css_colors
 description: Defines constant dart:ui Color objects for CSS colors (for use in Flutter code).
 repository: https://github.com/flutter/packages/tree/main/packages/css_colors
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+css_colors%22
-version: 1.1.3
+version: 1.1.4
 
 environment:
   sdk: ">=3.0.0 <4.0.0"
@@ -11,6 +11,8 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
+  flutter_test:
+    sdk: flutter
 
 topics:
   - color

packages/css_colors/test/css_colors_test.dart

@@ -0,0 +1,20 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:css_colors/css_colors.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('CSSColors.orange should be correct',
+      (WidgetTester tester) async {
+    // Create a Container widget using CSSColors.orange.
+    // #docregion Usage
+    final Container orange = Container(color: CSSColors.orange);
+    // #enddocregion Usage
+
+    // Ensure the color of the container is the expected one.
+    expect(orange.color, equals(const Color(0xFFFFA500)));
+  });
+}

script/configs/temp_exclude_excerpt.yaml

@@ -5,7 +5,6 @@
 
 # TODO(stuartmorgan): Remove everything from this list. See
 # https://github.com/flutter/flutter/issues/102679
-- css_colors
 - espresso
 - extension_google_sign_in_as_googleapis_auth
 - go_router_builder