Semi.Avalonia/demo/Semi.Avalonia.Demo/Pages/ExpanderDemo.axaml

<UserControl
    x:Class="Semi.Avalonia.Demo.Pages.ExpanderDemo"
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    d:DesignHeight="450"
    d:DesignWidth="800"
    mc:Ignorable="d">
    <StackPanel Spacing="20">
        <StackPanel>
            <Slider Name="SliderTest" Maximum="400" Minimum="0" TickFrequency="1" IsSnapToTickEnabled="True" />
            <Expander Header="Expander 1">
                <TextBlock Text="Hello Avalonia!" />
            </Expander>
            <Expander Header="Expander 2">
                <TextBox Text="Hello Avalonia!" />
            </Expander>
            <Expander Header="Expander 3">
                <Button Content="Hello Avalonia World!" />
            </Expander>
        </StackPanel>
        <Grid ColumnDefinitions="*, *">
            <Expander
                Height="200"
                ExpandDirection="Right"
                Header="Right">
                <TextBlock>Right Content</TextBlock>
            </Expander>
            <Expander
                Grid.Column="1"
                Height="200"
                HorizontalAlignment="Right"
                ExpandDirection="Left"
                Header="Left">
                <TextBlock>Left Content</TextBlock>
            </Expander>
        </Grid>
    </StackPanel>
</UserControl>