Extract themed properties and create simple and theme variants

src/AvaloniaEdit/AvaloniaEdit.xaml

@@ -1,11 +1,19 @@
 <Styles xmlns="https://github.com/avaloniaui">
 
-    <StyleInclude Source="avares://AvaloniaEdit/TextEditor.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/Editing/TextArea.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/CodeCompletion/CompletionList.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/CodeCompletion/InsightWindow.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/Rendering/VisualLineDrawingVisual.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/Search/DropDownButton.xaml" />
-    <StyleInclude Source="avares://AvaloniaEdit/Search/SearchPanel.xaml" />
+  <Styles.Resources>
+    <ResourceDictionary>
+      <ResourceDictionary.MergedDictionaries>
+        <MergeResourceInclude Source="/Themes/Fluent/Base.xaml" />
+      </ResourceDictionary.MergedDictionaries>
+    </ResourceDictionary>
+  </Styles.Resources>
+
+  <StyleInclude Source="avares://AvaloniaEdit/TextEditor.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/Editing/TextArea.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/CodeCompletion/CompletionList.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/CodeCompletion/InsightWindow.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/Rendering/VisualLineDrawingVisual.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/Search/DropDownButton.xaml" />
+  <StyleInclude Source="avares://AvaloniaEdit/Search/SearchPanel.xaml" />
 
 </Styles>

src/AvaloniaEdit/Search/SearchPanel.xaml

@@ -60,12 +60,12 @@
     <Style Selector="search|SearchPanel">
         <Setter Property="BorderThickness" Value="1 0 1 1" />
         <Setter Property="CornerRadius" Value="0 0 4 4" />
-        <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseLowBrush}" />
-        <Setter Property="Background" Value="{DynamicResource SystemControlBackgroundChromeMediumBrush}" />
+        <Setter Property="BorderBrush" Value="{DynamicResource SearchPanelBorderBrush}" />
+        <Setter Property="Background" Value="{DynamicResource SearchPanelBackgroundBrush}" />
         <Setter Property="Focusable" Value="True" />
         <Setter Property="Margin" Value="0 0 18 0" />
-        <Setter Property="FontSize" Value="{DynamicResource ControlContentThemeFontSize}" />
-        <Setter Property="FontFamily" Value="{DynamicResource ContentControlThemeFontFamily}" />
+        <Setter Property="FontSize" Value="{DynamicResource SearchPanelFontSize}" />
+        <Setter Property="FontFamily" Value="{DynamicResource SearchPanelFontFamily}" />
         <Setter Property="Template">
             <ControlTemplate>
                 <Border Name="PART_Border"

src/AvaloniaEdit/Themes/Fluent/Base.xaml

@@ -0,0 +1,16 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:sys="using:System">
+  <StaticResource x:Key="SearchPanelFontSize" ResourceKey="ControlContentThemeFontSize" />
+  <StaticResource x:Key="SearchPanelFontFamily" ResourceKey="ContentControlThemeFontFamily" />
+  <ResourceDictionary.ThemeDictionaries>
+    <ResourceDictionary x:Key="Default">
+      <SolidColorBrush x:Key="SearchPanelBackgroundBrush" Color="{DynamicResource SystemChromeMediumColor}" />
+      <SolidColorBrush x:Key="SearchPanelBorderBrush" Color="{DynamicResource SystemBaseLowColor}" />
+    </ResourceDictionary>
+    <ResourceDictionary x:Key="Dark">
+      <SolidColorBrush x:Key="SearchPanelBackgroundBrush" Color="{DynamicResource SystemChromeMediumColor}" />
+      <SolidColorBrush x:Key="SearchPanelBorderBrush" Color="{DynamicResource SystemBaseLowColor}" />
+    </ResourceDictionary>
+  </ResourceDictionary.ThemeDictionaries>
+</ResourceDictionary>

src/AvaloniaEdit/Themes/Simple/Base.xaml

@@ -0,0 +1,16 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:sys="using:System">
+    <StaticResource x:Key="SearchPanelFontSize" ResourceKey="FontSizeNormal" />
+    <StaticResource x:Key="SearchPanelFontFamily" ResourceKey="ContentControlThemeFontFamily" />
+    <ResourceDictionary.ThemeDictionaries>
+        <ResourceDictionary x:Key="Default">
+            <SolidColorBrush x:Key="SearchPanelBackgroundBrush" Color="{DynamicResource ThemeBackgroundColor}" />
+            <SolidColorBrush x:Key="SearchPanelBorderBrush" Color="{DynamicResource ThemeBorderLowColor}" />
+        </ResourceDictionary>
+        <ResourceDictionary x:Key="Dark">
+            <SolidColorBrush x:Key="SearchPanelBackgroundBrush" Color="{DynamicResource ThemeBackgroundColor}" />
+            <SolidColorBrush x:Key="SearchPanelBorderBrush" Color="{DynamicResource ThemeBorderLowColor}" />
+        </ResourceDictionary>
+    </ResourceDictionary.ThemeDictionaries>
+</ResourceDictionary>