Change Parent Control propery using Child Control in WPF

Question

I have a grid contains two TextBox's, and trying to change grid background color to red and green depends on the TextBox that get focus. However I couldn't make below snippets to work as Setter doesn't support TargetName property. Could anyone please provide a solution to achieve this in XAML

<Grid x:Name="grid">
    <StackPanel>
        <TextBox Width="300"
                 Height="40"
                 x:Name="txt1">
            <TextBox.Style>
                <Style TargetType="TextBox">
                    <Style.Triggers>
                        <Trigger Property="IsFocused"
                                 Value="True">
                            <Setter TargetName="grid"
                                    Property="Background"
                                    Value="Red" />
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </TextBox.Style>
        </TextBox>

        <TextBox Width="300"
                 Height="40"
                 x:Name="txt2">
            <TextBox.Style>
                <Style TargetType="TextBox">
                    <Style.Triggers>
                        <Trigger Property="IsFocused"
                                 Value="True">
                            <Setter TargetName="grid"
                                    Property="Background"
                                    Value="Green" />
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </TextBox.Style>
        </TextBox>
    </StackPanel>
</Grid>

Answer 1

I think one of the easiest ways is using Style.Triggers at Grid level with DataTrigger.

<Grid x:Name="grid">
    <Grid.Style>
        <Style TargetType="{x:Type Grid}">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ElementName=txt1, Path=IsFocused}" Value="True">
                    <Setter Property="Background" Value="Red" />
                </DataTrigger>
                <DataTrigger Binding="{Binding ElementName=txt2, Path=IsFocused}" Value="True">
                    <Setter Property="Background" Value="Green" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Grid.Style>
    <StackPanel>
        <TextBox Width="300"
                 Height="40"
                 x:Name="txt1"/>
        <TextBox Width="300"
                 Height="40"
                 x:Name="txt2"/>
    </StackPanel>
</Grid>