Improve selected text highlighting (#2938)

* Improve selected text highlighting

Signed-off-by: Konctantin <gawrilyako@gmail.com>

* Format code

Signed-off-by: Konctantin <gawrilyako@gmail.com>

---------

Signed-off-by: Konctantin <gawrilyako@gmail.com>

ILSpy/TextView/DecompilerTextView.xaml

@@ -5,12 +5,28 @@
 			 xmlns:controls="clr-namespace:ICSharpCode.ILSpy.Controls"
 			 xmlns:local="clr-namespace:ICSharpCode.ILSpy.TextView"
 			 xmlns:ae="clr-namespace:ICSharpCode.AvalonEdit;assembly=ICSharpCode.AvalonEdit"
+			 xmlns:editing="clr-namespace:ICSharpCode.AvalonEdit.Editing;assembly=ICSharpCode.AvalonEdit"
 			 xmlns:folding="clr-namespace:ICSharpCode.AvalonEdit.Folding;assembly=ICSharpCode.AvalonEdit"
 			 xmlns:styles="urn:TomsToolbox.Wpf.Styles"
 			 xmlns:themes="clr-namespace:ICSharpCode.ILSpy.Themes">
 	<UserControl.Resources>
 		<BooleanToVisibilityConverter x:Key="boolToVisibility" />
 		<SolidColorBrush x:Key="waitAdornerBackgoundBrush" Color="{DynamicResource {x:Static SystemColors.WindowColorKey}}" Opacity=".75"/>
+		<Style TargetType="{x:Type editing:TextArea}">
+			<Setter Property="FocusVisualStyle" Value="{x:Null}" />
+			<Setter Property="SelectionForeground" Value="{x:Null}" />
+			<Setter Property="SelectionCornerRadius" Value="0.0" />
+			<Setter Property="SelectionBrush">
+				<Setter.Value>
+					<SolidColorBrush Color="{DynamicResource {x:Static SystemColors.HighlightColorKey}}" Opacity="0.3" />
+				</Setter.Value>
+			</Setter>
+			<Setter Property="SelectionBorder">
+				<Setter.Value>
+					<Pen Brush="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" Thickness="0" />
+				</Setter.Value>
+			</Setter>
+		</Style>
 	</UserControl.Resources>
 	<Grid>
 		<Border BorderThickness="1,1,0,1" BorderBrush="{DynamicResource {x:Static SystemColors.ControlLightBrushKey}}">