Add min height for DropDownButton, same as ComboBox

samples/ControlCatalog/Pages/ButtonsPage.xaml

@@ -172,6 +172,7 @@
                   Width="32" />
         </DropDownButton>
         <DropDownButton IsEnabled="False">Disabled</DropDownButton>
+        <DropDownButton />
       </StackPanel>
     </Border>
 
@@ -197,7 +198,8 @@
           <TextBlock Text="Disabled" />
         </SplitButton>
         <SplitButton Flyout="{StaticResource SharedMenuFlyout}"
-                     Content="Re-themed">
+                     Content="Re-themed"
+                     Foreground="White">
           <SplitButton.Styles>
             <Style>
               <Style.Resources>

src/Avalonia.Themes.Fluent/Controls/ComboBox.xaml

@@ -106,6 +106,7 @@
                       Grid.Column="1"
                       UseLayoutRounding="False"
                       IsHitTestVisible="False"
+                      MinHeight="{DynamicResource ComboBoxMinHeight}"
                       Height="12"
                       Width="12"
                       Margin="0,0,10,0"

src/Avalonia.Themes.Fluent/Controls/DropDownButton.xaml

@@ -11,6 +11,10 @@
     </Border>
   </Design.PreviewWith>
 
+  <Styles.Resources>
+    <x:Double x:Key="DropDownButtonMinHeight">32</x:Double>
+  </Styles.Resources>
+  
   <Style Selector="DropDownButton">
     <Setter Property="Background" Value="{DynamicResource ButtonBackground}" />
     <Setter Property="Foreground" Value="{DynamicResource ButtonForeground}" />
@@ -29,7 +33,8 @@
                   Background="{TemplateBinding Background}"
                   BorderBrush="{TemplateBinding BorderBrush}"
                   BorderThickness="{TemplateBinding BorderThickness}"
-                  CornerRadius="{TemplateBinding CornerRadius}">
+                  CornerRadius="{TemplateBinding CornerRadius}"
+                  ClipToBounds="True">
             <Grid x:Name="InnerGrid">
               <Grid.ColumnDefinitions>
                 <ColumnDefinition Width="*" />
@@ -49,6 +54,7 @@
                         Grid.Column="1"
                         UseLayoutRounding="False"
                         IsHitTestVisible="False"
+                        MinHeight="{DynamicResource DropDownButtonMinHeight}"
                         Height="12"
                         Width="12"
                         Margin="0,0,10,0"