Avalonia/samples/ControlCatalog/Pages/ExpanderPage.xaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:viewModels="using:ControlCatalog.ViewModels"
             x:Class="ControlCatalog.Pages.ExpanderPage"
             x:DataType="viewModels:ExpanderPageViewModel">
  <StackPanel Orientation="Vertical" Spacing="4">
    <TextBlock Classes="h2">Expands to show nested content</TextBlock>

    <StackPanel Orientation="Vertical"
                Margin="0,16,0,0"
                HorizontalAlignment="Center"
                Spacing="16">
      <Expander Header="Expand Up" ExpandDirection="Up"
                CornerRadius="{Binding CornerRadius}">
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <Expander Header="Expand Down" ExpandDirection="Down"
                CornerRadius="{Binding CornerRadius}">
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <Expander Header="Expand Left" ExpandDirection="Left"
                CornerRadius="{Binding CornerRadius}">
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <Expander Header="Expand Right" ExpandDirection="Right"
                CornerRadius="{Binding CornerRadius}">
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <Expander ExpandDirection="Down"
                CornerRadius="{Binding CornerRadius}">
        <Expander.Header>
          <Button Content="Control in Header" />
        </Expander.Header>
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <Expander Header="Disabled"
                IsEnabled="False"
                ExpandDirection="Down"
                CornerRadius="{Binding CornerRadius}">
        <StackPanel>
          <TextBlock>Expanded content</TextBlock>
        </StackPanel>
      </Expander>
      <CheckBox IsChecked="{Binding Rounded}">Rounded</CheckBox>
    </StackPanel>
  </StackPanel>
</UserControl>