How do I change the background of my Grid layout when one of it’s children gets keyboard focus?

You can change the background of the grid layout when one of its children gets keyboard focus by setting the IsKeyboardFocusWithin property. This can be done with the following code snippet,

[XAML]
<Window.Resources>
        <Style x:Key = "GridTriggerStyle" TargetType = "Grid">
            <Style.Triggers>
                <Trigger Property = "IsKeyboardFocusWithin" Value = "True">
                    <Setter Property = "Background" Value = "Green" />
                </Trigger>
                <Trigger Property = "IsKeyboardFocusWithin" Value = "False">
                    <Setter Property = "Background" Value = "AliceBlue" />
                </Trigger>
            </Style.Triggers>
       </Style>
    </Window.Resources>
     
    <Grid Name="testGrid" Style="{StaticResource GridTriggerStyle}">
        <Button Height="30" Width="100" Content="SampleButton1"/>
    </Grid>