Decorators: The all content controls like ScrollViewer, GroupBox,
Expander are very helpful tools to make an effective WPF application these al
are designing tools. There is one type or you can say branch of container is
available in WPF which is use to perform graphical changes on an object. These
branch of container is also called the Elements of the container and the WPF
call these Decorators.
The System.Windows.Controls.Decorator is provide the functionality to all the
decorators. All the decorators are derive from this. Generally all decorators
are used for designing and working with controls. In WPF we use many decorators
like ButtonChorme decorator is used with button to change its shape and
background, one more decorators is ListBoxChorme decorator, it is used with
ListBox.
For better and deep understanding I explain two main decorator of WPF. That's
two general decorators are Border and Viewbox.
Border: We use Border to display a border around your content, and for
that we must place the elements within a parent Border
element. Border can have only one child. To
display multiple child elements, you need to place an additional panel element
within the parent Border. You can then place child
elements within that panel element.
Example of Border Decorator
<Window
x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow"
Height="350"
Width="525">
<Border
Margin="5"
Padding="5"
Background="LightYellow"
BorderBrush="Blue"
BorderThickness="5,5,6,5"
CornerRadius="3"
VerticalAlignment="Top">
<StackPanel>
<Button
Margin="3">Manish</Button>
<Button
Margin="3">sapna</Button>
<Button
Margin="3">Tewatia</Button>
<Button
Margin="3">Beniwal</Button>
</StackPanel>
</Border>
</Window>
Output Window

Conclusion
Hope this article helps you to
understand the Decorators in WPF.