feat: Add a theme for HeaderedContentControl as GroupBox.

demo/Semi.Avalonia.Demo/Pages/HeaderedContentControlDemo.axaml

@@ -0,0 +1,12 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="Semi.Avalonia.Demo.Pages.HeaderedContentControlDemo">
+    <ScrollViewer>
+        <HeaderedContentControl Header="Semi Design">
+            <TextBlock TextWrapping="Wrap">Semi Design 是由互娱社区前端团队与 UED 团队共同设计开发并维护的设计系统。设计系统包含设计语言以及一整套可复用的前端组件，帮助设计师与开发者更容易地打造高质量的、用户体验一致的、符合设计规范的 Web 应用。</TextBlock>
+        </HeaderedContentControl>
+    </ScrollViewer>
+</UserControl>

demo/Semi.Avalonia.Demo/Pages/HeaderedContentControlDemo.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace Semi.Avalonia.Demo.Pages;
+
+public partial class HeaderedContentControlDemo : UserControl
+{
+    public HeaderedContentControlDemo()
+    {
+        InitializeComponent();
+    }
+}

demo/Semi.Avalonia.Demo/Views/MainView.axaml

@@ -123,6 +123,9 @@
             <TabItem Header="GridSplitter">
                 <pages:GridSplitter />
             </TabItem>
+            <TabItem Header="HeaderedContentControl">
+                <pages:HeaderedContentControlDemo />
+            </TabItem>
             <TabItem Header="Label">
                 <pages:LabelDemo />
             </TabItem>