I want to create a ScrollView that only shows the horizontal scroll bar when the mouse is over it, so I tried the following (note how I simply try to trigger the HorizontalScrollBarVisibility to Auto when the mouse is over and predefine my ScrollViewer to have a Disabled HorizontalScrollBarVisibility):

```
<Window x:Class="OnMouseOverStackPanel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Style x:Key="Triggers" TargetType="ScrollViewer">
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="true">
                    <Setter Property="HorizontalScrollBarVisibility" Value="Auto"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Button Grid.Row="0" Content="I'm a content filler."/>
        <ScrollViewer Grid.Row="1" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Disabled" Style="{StaticResource Triggers}">
            <StackPanel Orientation="Horizontal" Height="30">
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
                <Button Content="Hey, I'm a button!"/>
            </StackPanel>
        </ScrollViewer>
        <Button Grid.Row="2" Content="I'm a content filler."/>
    </Grid>
</Window>

```

Unfortunately this isn't working for me. How can I append triggers to this object to get it to work?