diff --git a/src/Perspex.Controls/GridSplitter.cs b/src/Perspex.Controls/GridSplitter.cs
index efb50c3e72..35c118de81 100644
--- a/src/Perspex.Controls/GridSplitter.cs
+++ b/src/Perspex.Controls/GridSplitter.cs
@@ -4,8 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-
-using Perspex.Collections;
 using Perspex.Controls.Primitives;
 using Perspex.Input;
 using Perspex.VisualTree;
@@ -32,8 +30,6 @@ namespace Perspex.Controls
 
         private DefinitionBase _nextDefinition;
 
-        private bool _isResizingColumns;
-
         private List<DefinitionBase> _definitions;
 
         /// <summary>
@@ -52,7 +48,10 @@ namespace Perspex.Controls
                 SetValue(OrientationProperty, value);
             }
         }
-        
+
+        /// <summary>
+        /// Initializes static members of the <see cref="GridSplitter"/> class. 
+        /// </summary>
         static GridSplitter()
         {
             PseudoClass(OrientationProperty, o => o == Perspex.Controls.Orientation.Vertical, ":vertical");
diff --git a/src/Perspex.Controls/Primitives/ScrollBar.cs b/src/Perspex.Controls/Primitives/ScrollBar.cs
index 8e26275fe8..9b079bfa4c 100644
--- a/src/Perspex.Controls/Primitives/ScrollBar.cs
+++ b/src/Perspex.Controls/Primitives/ScrollBar.cs
@@ -31,6 +31,15 @@ namespace Perspex.Controls.Primitives
         public static readonly StyledProperty<Orientation> OrientationProperty =
             PerspexProperty.Register<ScrollBar, Orientation>(nameof(Orientation));
 
+        /// <summary>
+        /// Initializes static members of the <see cref="ScrollBar"/> class. 
+        /// </summary>
+        static ScrollBar()
+        {
+            PseudoClass(OrientationProperty, o => o == Perspex.Controls.Orientation.Vertical, ":vertical");
+            PseudoClass(OrientationProperty, o => o == Perspex.Controls.Orientation.Horizontal, ":horizontal");
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ScrollBar"/> class.
         /// </summary>
diff --git a/src/Perspex.Controls/Slider.cs b/src/Perspex.Controls/Slider.cs
index 575690af74..30b498e80f 100644
--- a/src/Perspex.Controls/Slider.cs
+++ b/src/Perspex.Controls/Slider.cs
@@ -3,7 +3,6 @@
 
 using System;
 using Perspex.Controls.Primitives;
-using Perspex.Controls.Templates;
 using Perspex.Input;
 using Perspex.Interactivity;
 
@@ -40,6 +39,8 @@ namespace Perspex.Controls
         /// </summary>
         static Slider()
         {
+            PseudoClass(OrientationProperty, o => o == Perspex.Controls.Orientation.Vertical, ":vertical");
+            PseudoClass(OrientationProperty, o => o == Perspex.Controls.Orientation.Horizontal, ":horizontal");
             Thumb.DragStartedEvent.AddClassHandler<Slider>(x => x.OnThumbDragStarted, RoutingStrategies.Bubble);
             Thumb.DragDeltaEvent.AddClassHandler<Slider>(x => x.OnThumbDragDelta, RoutingStrategies.Bubble);
             Thumb.DragCompletedEvent.AddClassHandler<Slider>(x => x.OnThumbDragCompleted, RoutingStrategies.Bubble);
diff --git a/src/Perspex.Themes.Default/ScrollBar.paml b/src/Perspex.Themes.Default/ScrollBar.paml
index de0aa2fd4c..fa1f1d9d18 100644
--- a/src/Perspex.Themes.Default/ScrollBar.paml
+++ b/src/Perspex.Themes.Default/ScrollBar.paml
@@ -20,16 +20,16 @@
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="ScrollBar[Orientation=Horizontal]">
+  <Style Selector="ScrollBar:horizontal">
     <Setter Property="Height" Value="10"/>
   </Style>
-  <Style Selector="ScrollBar[Orientation=Horizontal] /template/ Thumb#thumb">
+  <Style Selector="ScrollBar:horizontal /template/ Thumb#thumb">
     <Setter Property="MinWidth" Value="10"/>
   </Style>
-  <Style Selector="ScrollBar[Orientation=Vertical]">
+  <Style Selector="ScrollBar:vertical">
     <Setter Property="Width" Value="10"/>
   </Style>
-  <Style Selector="ScrollBar[Orientation=Vertical] /template/ Thumb#thumb">
+  <Style Selector="ScrollBar:vertical /template/ Thumb#thumb">
     <Setter Property="MinHeight" Value="10"/>
   </Style>
 </Styles>
\ No newline at end of file
diff --git a/src/Perspex.Themes.Default/Slider.paml b/src/Perspex.Themes.Default/Slider.paml
index 8d8ef0ce18..dbdc96aaec 100644
--- a/src/Perspex.Themes.Default/Slider.paml
+++ b/src/Perspex.Themes.Default/Slider.paml
@@ -1,5 +1,5 @@
 <Styles xmlns="https://github.com/perspex">
-  <Style Selector="Slider[Orientation=Horizontal]">
+  <Style Selector="Slider:horizontal">
     <Setter Property="MinWidth" Value="40"/>
     <Setter Property="MinHeight" Value="20"/>
     <Setter Property="Template">
@@ -26,7 +26,7 @@
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="Slider[Orientation=Vertical]">
+  <Style Selector="Slider:vertical">
     <Setter Property="MinWidth" Value="20"/>
     <Setter Property="MinHeight" Value="40"/>
     <Setter Property="Template">