essayez ceci
<DataGrid.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Transparent"/>
<Style TargetType="{x:Type DataGridRow}">
<Setter Property="HeaderStyle">
<Setter.Value>
<Style TargetType="{x:Type DataGridRowHeader}">
<Setter Property="Visibility" Value="Collapsed"/>
<Setter Property="Width" Value="0"/>
</Style>
</Setter.Value>
</Setter>
<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="Validation.ErrorTemplate" Value="{x:Null}"/>
<Setter Property="ValidationErrorTemplate">
<Setter.Value>
<ControlTemplate>
<TextBlock Foreground="Red" Margin="2,0,0,0" Text="!" VerticalAlignment="Center"/>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type DataGridRow}">
<Border x:Name="DGR_Border" BorderThickness="1" CornerRadius="5" Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
<SelectiveScrollingGrid>
<SelectiveScrollingGrid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</SelectiveScrollingGrid.ColumnDefinitions>
<Grid Grid.Column="1">
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<DataGridCellsPresenter ItemsPanel="{TemplateBinding ItemsPanel}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
<DataGridDetailsPresenter Margin="4" Grid.Row="1" SelectiveScrollingGrid.SelectiveScrollingOrientation="{Binding AreRowDetailsFrozen, ConverterParameter={x:Static SelectiveScrollingOrientation.Vertical}, Converter={x:Static DataGrid.RowDetailsScrollingConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" Visibility="{TemplateBinding DetailsVisibility}"/>
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.RowSpan="2"/>
</Grid>
<DataGridRowHeader SelectiveScrollingGrid.SelectiveScrollingOrientation="Vertical" Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.Row}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
</SelectiveScrollingGrid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter TargetName="DGR_Border" Property="BorderBrush" Value="Blue"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="DetailsVisibility" Value="Visible">
<Setter Property="BorderThickness" Value="4,1,4,4"/>
<Setter Property="BorderBrush" Value="#FF3886B9"/>
</Trigger>
<!--<Trigger Property="IsSelected" Value="True">
<Setter Property="BorderBrush" Value="Blue"/>
</Trigger>-->
</Style.Triggers>
</Style>
</DataGrid.Resources>