WPF how can i get focus from ScrollViewer ScrollContentPresenter - wpf

Question

that ScrollViewer.IsFocused set to true only if i click the border of ScrollViewer , not input a text in the TextBox or click the inside content,how can i get the focus to change the background.
<Style x:Key="ScrollViewerStyle" TargetType="{x:Type ScrollViewer}">
<Setter Property="OverridesDefaultStyle" Value="True" />
<Setter Property="VerticalAlignment" Value="Stretch"/>
<Setter Property="HorizontalAlignment" Value="Stretch"/>
<Setter Property="FontSize" Value="14"/>
<Setter Property="Foreground" Value="White"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ScrollViewer}">
<DockPanel>
<Border x:Name="border" BorderBrush="{Binding L1, Source={x:Static color:DesignBrushCollection.DesignColors}}" BorderThickness="1">
<Grid x:Name="Grid">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="auto"/>
</Grid.ColumnDefinitions>
<Grid x:Name="text" Background="{Binding BG3, Source={x:Static color:DesignBrushCollection.DesignColors}}">
<ScrollContentPresenter x:Name="PART_ScrollContentPresenter"
CanContentScroll="{TemplateBinding CanContentScroll}" CanHorizontallyScroll="False" CanVerticallyScroll="False" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="0" Margin="{TemplateBinding Padding}" />
</Grid>
<ScrollBar x:Name="PART_VerticalScrollBar" AutomationProperties.AutomationId="VerticalScrollBar" Cursor="Arrow" Grid.Column="1" Maximum="{TemplateBinding ScrollableHeight}" Minimum="0" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportHeight}"
Style="{DynamicResource ScrollBarStyle}"/>
</Grid>
</Border>
</DockPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="BorderBrush" TargetName="border"
Value="{Binding AC3, Source={x:Static color:DesignBrushCollection.DesignColors}}"/>
</Trigger>
<Trigger Property="IsFocused" Value="true">
<Setter Property="BorderBrush" TargetName="border"
Value="{Binding AC3, Source={x:Static color:DesignBrushCollection.DesignColors}}"/>
<Setter Property="Background" TargetName="text"
Value="{Binding BG1, Source={x:Static color:DesignBrushCollection.DesignColors}}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Opacity" Value="0.5"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

Instead of IsFocused property you should use property IsKeyboardFocusWithin in the Trigger, this will apply appropriate Setters, if any child control of ScrollViewer has a keyboard focus.
<Trigger Property="IsKeyboardFocusWithin" Value="true">