wallpaper selector: style the scrollbar

.config/quickshell/ii/modules/common/widgets/StyledScrollBar.qml

@@ -0,0 +1,26 @@
+import QtQuick
+import QtQuick.Controls
+import qs.modules.common
+import qs.modules.common.functions
+
+ScrollBar {
+    id: root
+
+    policy: ScrollBar.AsNeeded
+
+    contentItem: Rectangle {
+        implicitWidth: 4
+        implicitHeight: root.visualSize
+        radius: width / 2
+        color: Appearance.colors.colOnSurfaceVariant
+        
+        opacity: root.policy === ScrollBar.AlwaysOn || (root.active && root.size < 1.0) ? 0.5 : 0
+        Behavior on opacity {
+            NumberAnimation {
+                duration: 350
+                easing.type: Appearance.animation.elementMoveFast.type
+                easing.bezierCurve: Appearance.animation.elementMoveFast.bezierCurve
+            }
+        }
+    }
+}

.config/quickshell/ii/modules/wallpaperSelector/WallpaperSelectorContent.qml

@@ -204,9 +204,7 @@ Item {
                         boundsBehavior: Flickable.StopAtBounds
                         bottomMargin: extraOptions.implicitHeight
 
-                        ScrollBar.vertical: ScrollBar {
-                            policy: ScrollBar.AsNeeded
-                        }
+                        ScrollBar.vertical: StyledScrollBar {}
 
                         function moveSelection(delta) {
                             currentIndex = Math.max(0, Math.min(grid.model.count - 1, currentIndex + delta));