How to remove the border of a ContentControl - wpf

Question

I have a DataTemplateSelector like this:
Public Class TestTemplateSelector
Inherits DataTemplateSelector
Public Property Template1 As DataTemplate
Public Property Template2 As DataTemplate
Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) As DataTemplate
Dim selector As Integer
If (item Is Nothing) OrElse TypeOf item IsNot String Then
Return MyBase.SelectTemplate(item, container)
End If
If Not Integer.TryParse(CType(item, String), selector) Then
Return MyBase.SelectTemplate(item, container)
End If
Select Case selector
Case 1
Return Me.Template1
Case 2
Return Me.Template2
Case Else
Return MyBase.SelectTemplate(item, container)
End Select
End Function
End Class
I define it in the Resources of a Window like this:
<Window.Resources>
<DataTemplate x:Key="Template1">
<TextBox Text="Template 1" />
</DataTemplate>
<DataTemplate x:Key="Template2">
<TextBox Text="Template 2" />
</DataTemplate>
<local:TestTemplateSelector x:Key="sel"
Template1="{StaticResource Template1}"
Template2="{StaticResource Template2}" />
</Window.Resources>
And I use it in the same Window like this:
<ContentControl Margin="5"
Content="2"
ContentTemplateSelector="{StaticResource sel}" />
If I switch the Content of the ContentControl between 1 and 2 it shows the corresponding templates, but I always see a gray border around the ContentControl.
Setting the BorderBrush of the ContentControl to Transparent and/or setting the BorderThickness to 0 doesn't remove the border.
How can I get rid of this border?
Here's a screenshot of the whole window:

Answer 1

There should be no border by default. You may have an implicit Style somewhere that adds it.
Try to set the BorderThickness property to 0:
<ContentControl Margin="5"
BorderThickness="0"
BorderBrush="{x:Null}"
Content="2"
ContentTemplateSelector="{StaticResource sel}" />
Or set the Template property to a ControlTemplate without a Border:
<ContentControl Margin="5"
Content="2"
ContentTemplateSelector="{StaticResource sel}">
<ContentControl.Template>
<ControlTemplate TargetType="{x:Type ContentControl}">
<ContentPresenter/>
</ControlTemplate>
</ContentControl.Template>
</ContentControl>