Improve visuals of BasicSliderBar focus

Author: peppy

osu.Framework.Tests/Visual/UserInterface/TestSceneSliderBar.cs

@@ -59,7 +59,7 @@ public TestSceneSliderBar()
                         Size = new Vector2(200, 50),
                         BackgroundColour = Color4.White,
                         SelectionColour = Color4.Pink,
-                        FocusColour = Color4.Purple,
+                        FocusColour = Color4.OrangeRed,
                         KeyboardStep = 1,
                         Current = sliderBarValue
                     },
@@ -73,7 +73,7 @@ public TestSceneSliderBar()
                         RangePadding = 20,
                         BackgroundColour = Color4.White,
                         SelectionColour = Color4.Pink,
-                        FocusColour = Color4.Purple,
+                        FocusColour = Color4.OrangeRed,
                         KeyboardStep = 1,
                         Current = sliderBarValue
                     },
@@ -87,7 +87,7 @@ public TestSceneSliderBar()
                         Size = new Vector2(200, 10),
                         BackgroundColour = Color4.White,
                         SelectionColour = Color4.Pink,
-                        FocusColour = Color4.Purple,
+                        FocusColour = Color4.OrangeRed,
                         KeyboardStep = 1,
                         Current = sliderBarValue
                     },
@@ -100,7 +100,7 @@ public TestSceneSliderBar()
                         Size = new Vector2(200, 10),
                         BackgroundColour = Color4.White,
                         SelectionColour = Color4.Pink,
-                        FocusColour = Color4.Purple,
+                        FocusColour = Color4.OrangeRed,
                         KeyboardStep = 1,
                         Current = sliderBarValue
                     },

osu.Framework/Graphics/UserInterface/BasicSliderBar.cs

@@ -18,16 +18,10 @@ public Color4 BackgroundColour
             set => Box.Colour = value;
         }
 
-        private Color4 selectionColour = FrameworkColour.Yellow;
-
         public Color4 SelectionColour
         {
-            get => selectionColour;
-            set
-            {
-                selectionColour = value;
-                updateColour();
-            }
+            get => SelectionBox.Colour;
+            set => SelectionBox.Colour = value;
         }
 
         private Color4 focusColour = FrameworkColour.YellowGreen;
@@ -38,7 +32,7 @@ public Color4 FocusColour
             set
             {
                 focusColour = value;
-                updateColour();
+                updateFocus();
             }
         }
 
@@ -56,30 +50,39 @@ public BasicSliderBar()
                 },
                 SelectionBox = new Box
                 {
+                    Colour = FrameworkColour.Yellow,
                     RelativeSizeAxes = Axes.Both,
                 }
             };
 
-            updateColour();
-        }
-
-        private void updateColour()
-        {
-            SelectionBox.Colour = HasFocus ? FocusColour : SelectionColour;
+            Masking = true;
         }
 
         protected override void OnFocus(FocusEvent e)
         {
-            updateColour();
+            updateFocus();
             base.OnFocus(e);
         }
 
         protected override void OnFocusLost(FocusLostEvent e)
         {
-            updateColour();
+            updateFocus();
             base.OnFocusLost(e);
         }
 
+        private void updateFocus()
+        {
+            if (HasFocus)
+            {
+                BorderThickness = 3;
+                BorderColour = FocusColour;
+            }
+            else
+            {
+                BorderThickness = 0;
+            }
+        }
+
         protected override void UpdateValue(float value)
         {
             SelectionBox.ScaleTo(new Vector2(value, 1), 300, Easing.OutQuint);