Set control adorner from xaml in Avalonia
<Button Content="Adorned Button"
HorizontalAlignment="Stretch" HorizontalContentAlignment="Center"
VerticalContentAlignment="Center" VerticalAlignment="Stretch"
Width="200" Height="42">
<XamlAdornerLayer.Adorner>
<Canvas x:Name="AdornerCanvas"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
Background="Cyan"
IsHitTestVisible="False"
Opacity="0.3"
IsVisible="True">
<Line StartPoint="-10000,0" EndPoint="10000,0" Stroke="Cyan" StrokeThickness="1" />
<Line StartPoint="-10000,42" EndPoint="10000,42" Stroke="Cyan" StrokeThickness="1" />
<Line StartPoint="0,-10000" EndPoint="0,10000" Stroke="Cyan" StrokeThickness="1" />
<Line StartPoint="200,-10000" EndPoint="200,10000" Stroke="Cyan" StrokeThickness="1" />
</Canvas>
</XamlAdornerLayer.Adorner>
</Button>