restore removed code.

samples/ControlCatalog/App.xaml

@@ -4,7 +4,29 @@
              x:DataType="vm:ApplicationViewModel"
              x:CompileBindings="True"
              x:Class="ControlCatalog.App">
-
+  <Application.Styles>
+    <Style Selector="TextBlock.h1">
+      <Setter Property="FontSize" Value="16" />
+      <Setter Property="FontWeight" Value="Medium" />
+    </Style>
+    <Style Selector="TextBlock.h2">
+      <Setter Property="FontSize" Value="14" />
+    </Style>
+    <Style Selector="TextBlock.h3">
+      <Setter Property="FontSize" Value="12" />
+    </Style>
+    <Style Selector="Label.h1">
+      <Setter Property="FontSize" Value="16" />
+      <Setter Property="FontWeight" Value="Medium" />
+    </Style>
+    <Style Selector="Label.h2">
+      <Setter Property="FontSize" Value="14" />
+    </Style>
+    <Style Selector="Label.h3">
+      <Setter Property="FontSize" Value="12" />
+    </Style>
+    <StyleInclude Source="/SideBar.xaml"/>
+  </Application.Styles>
   <TrayIcon.TrayIcons>
     <TrayIcons>
       <TrayIcon Icon="/Assets/test_icon.ico" ToolTipText="Avalonia Tray Icon ToolTip">