Next Gen UI demo (#1778)

First pass at a Next Generation UI demo app. The UI needs work, feedback
gratefully accepted.

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

next_gen_ui_demo/lib/styles.dart

@@ -0,0 +1,35 @@
+// Copyright 2023 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:flutter/material.dart';
+
+class TextStyles {
+  static const _font1 = TextStyle(fontFamily: 'Exo', color: Colors.white);
+
+  static TextStyle get h1 => _font1.copyWith(
+      fontSize: 75, letterSpacing: 35, fontWeight: FontWeight.w700);
+  static TextStyle get h2 => h1.copyWith(fontSize: 40, letterSpacing: 0);
+  static TextStyle get h3 =>
+      h1.copyWith(fontSize: 24, letterSpacing: 20, fontWeight: FontWeight.w400);
+  static TextStyle get body => _font1.copyWith(fontSize: 16);
+  static TextStyle get btn => _font1.copyWith(
+        fontSize: 16,
+        fontWeight: FontWeight.bold,
+        letterSpacing: 10,
+      );
+}
+
+abstract class AppColors {
+  static const orbColors = [
+    Color(0xFF71FDBF),
+    Color(0xFFCE33FF),
+    Color(0xFFFF5033),
+  ];
+
+  static const emitColors = [
+    Color(0xFF96FF33),
+    Color(0xFF00FFFF),
+    Color(0xFFFF993E),
+  ];
+}