Problems with databinding/datatrigger?

Hi,

I am trying/testing the XAML that were shown in one of the lessons of the CBT-nuggets for the exam 70-511.

When I select the option 'one' from the combobox, it should set the text 'you have selected one' to the textbox.
But this is not working.

What have I missed?

Thanks in advance.

Code:

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<Window x:Class="WpfApplication6.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">
    <Grid>
        <Grid.Resources>
            <Style TargetType="{x:Type Label}">
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="pink"/>
                    </Trigger>
                </Style.Triggers>
            </Style>
            <Style TargetType="{x:Type TextBox}">
                <Style.Triggers>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="IsMouseOver" Value="True" />
                            <Condition Property="Text" Value="" />
                        </MultiTrigger.Conditions>
                        <Setter Property="Background" Value="Aqua"/>
                    </MultiTrigger>
                </Style.Triggers>
            </Style>
        </Grid.Resources>
        <Label Content="Hover over me" Margin="5,0,392,287" />
        <Label Content="Hover over me also" Height="27" HorizontalAlignment="Left" Margin="5,30,0,0" Name="label1" VerticalAlignment="Top" Width="120" />
        <TextBox Height="23" HorizontalAlignment="Left" Margin="12,63,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" />
        <ComboBox Name="combo" Height="22" HorizontalAlignment="Left" Margin="12,92,0,0" VerticalAlignment="Top" Width="134">
            <ComboBoxItem Content="one" />
            <ComboBoxItem Content="two" />
            <ComboBoxItem Content="three" />
        </ComboBox>
        <TextBox IsReadOnly="True" DataContext="{Binding ElementName=combo, Path=SelectedItem}"  Height="22" HorizontalAlignment="Left" Margin="152,92,0,0" VerticalAlignment="Top" Width="152">
            <TextBox.Resources>
                <Style TargetType="{x:Type TextBox}">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding}" Value="one">
                    <Setter Property="Text" Value="You have selected one" />
                    </DataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBox.Resources>
        </TextBox>
       
    </Grid>
</Window>

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