Improve AutoCompleteBox border (#6)

* fix: unify autocompletebox border with textbox.

* feat: reduce padding, improve demo.

Author: rabbitism

samples/Classic.Demo/MainWindow.axaml

@@ -300,6 +300,13 @@
           <TextBox Text="Lorem ipsum dolor sit amet.."/>
           <ComboBox ItemsSource="abcdefgh" SelectedIndex="1" />
           <ComboBox ItemsSource="abcdefgh" IsEnabled="False" SelectedIndex="0" />
+          <AutoCompleteBox ItemsSource="{Binding People}" ValueMemberBinding="{Binding FirstName}">
+            <AutoCompleteBox.ItemTemplate>
+              <DataTemplate x:DataType="demo:PersonViewModel">
+                <TextBlock Text="{Binding FirstName}"/>
+              </DataTemplate>
+            </AutoCompleteBox.ItemTemplate>
+          </AutoCompleteBox>
         </StackPanel>
       </TabItem>
       <TabItem Header="Buttons">

src/Classic.Avalonia.Theme/Styles/AutoCompleteBox.axaml

@@ -1,12 +1,13 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:common="clr-namespace:Classic.CommonControls;assembly=Classic.CommonControls.Avalonia"
                     x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type AutoCompleteBox}"
                 TargetType="AutoCompleteBox">
-    <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
-    <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}" />
-    <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}" />
-    <Setter Property="Padding" Value="4" />
+    <Setter Property="Background" Value="{DynamicResource {x:Static common:SystemColors.WindowBrushKey}}" />
+    <Setter Property="BorderBrush" Value="{x:Static ClassicBorderDecorator.ClassicBorderBrush}" />
+    <Setter Property="BorderThickness" Value="2" />
+    <Setter Property="Padding" Value="1" />
     <Setter Property="Template">
       <ControlTemplate>
         <Panel>