feat: add backward compatibility.

demo/Semi.Avalonia.Demo/App.axaml

@@ -4,6 +4,9 @@
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:semi="https://irihi.tech/semi">
     <Application.Styles>
+        <!-- You can still reference in old way. 
+        <StyleInclude Source="avares://Semi.Avalonia/Themes/Index.axaml" />
+         -->
         <semi:SemiTheme Locale="zh-CN"/>
         <StyleInclude Source="avares://Semi.Avalonia.DataGrid/Index.axaml" />
         <StyleInclude Source="avares://Semi.Avalonia.ColorPicker/Index.axaml" />

src/Semi.Avalonia/Themes/Index.axaml

@@ -1,4 +1,4 @@
-<Styles x:Class="Semi.Avalonia.SemiTheme" xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <Styles.Resources>
         <ResourceDictionary>
             <ResourceDictionary.ThemeDictionaries>

src/Semi.Avalonia/Themes/SemiTheme.axaml

@@ -0,0 +1,19 @@
+<Styles x:Class="Semi.Avalonia.SemiTheme" xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <Styles.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.ThemeDictionaries>
+                <MergeResourceInclude x:Key="Default" Source="avares://Semi.Avalonia/Themes/Light/_index.axaml" />
+                <MergeResourceInclude x:Key="Dark" Source="avares://Semi.Avalonia/Themes/Dark/_index.axaml" />
+            </ResourceDictionary.ThemeDictionaries>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceInclude Source="avares://Semi.Avalonia/Controls/_index.axaml" />
+                <ResourceInclude Source="avares://Semi.Avalonia/Themes/Base.axaml" />
+                <ResourceInclude Source="avares://Semi.Avalonia/Themes/Shared/_index.axaml" />
+                <ResourceInclude Source="avares://Semi.Avalonia/Locale/zh-cn.axaml" />
+            </ResourceDictionary.MergedDictionaries>
+        </ResourceDictionary>
+    </Styles.Resources>
+    <Style Selector=":is(UserControl)">
+        <Setter Property="Theme" Value="{DynamicResource {x:Type UserControl}}" />
+    </Style>
+</Styles>