How to avoid WPF window reduces its dimension - wpf

Question

I read a few post but I can't fix this problem.
I have a Grid defined as follow:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="2*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
...
Where in the first row I want a Border with a TextBlock inside. I need that the Border has always the same size without be influenced from the TextBlock.
<Grid Grid.Row="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Border Grid.Row="0" BorderBrush="{DynamicResource StandardBorderColor}" BorderThickness="2" Margin="15,10,15,10"
HorizontalAlignment="Stretch"/>
<TextBlock Grid.Row="0" Name="TextBlock" Margin="20, 15, 20, 20"
TextWrapping="Wrap" Foreground="{DynamicResource StandardForegroundColor}" FontSize="18" FontWeight="Bold"
VerticalAlignment="Center" TextAlignment="Left" Text="{Binding Testo}" HorizontalAlignment="Stretch"/>
</Grid>
Do you have any suggestions? Thanks in advance!
Update:
Solution:
I found this as solution:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="2*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<GroupBox HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch"
VerticalAlignment="Stretch" VerticalContentAlignment="Stretch"
Margin="15, 10, 15, 10" Header="Avvisi">
<TextBox x:Name="TextBlock" FontSize="16"
VerticalContentAlignment="Stretch" HorizontalContentAlignment="Stretch"
TextAlignment="Left" Text="{Binding Testo}" Style="{DynamicResource TxtBoxStyle}" ScrollViewer.VerticalScrollBarVisibility="Visible"
BorderBrush="Transparent" IsReadOnly="True" />
</GroupBox>
...