dock: add opacity slider as requested in #222

Modules/SettingsPanel/Tabs/GeneralTab.qml

@@ -77,6 +77,45 @@ ColumnLayout {
       onToggled: checked => Settings.data.dock.autoHide = checked
     }
 
+    ColumnLayout {
+      spacing: Style.marginXXS * scaling
+      Layout.fillWidth: true
+
+      NText {
+        text: "Dock Background Opacity"
+        font.pointSize: Style.fontSizeL * scaling
+        font.weight: Style.fontWeightBold
+        color: Color.mOnSurface
+      }
+
+      NText {
+        text: "Adjust the background opacity of the dock."
+        font.pointSize: Style.fontSizeXS * scaling
+        color: Color.mOnSurfaceVariant
+        wrapMode: Text.WordWrap
+        Layout.fillWidth: true
+      }
+
+      RowLayout {
+        NSlider {
+          Layout.fillWidth: true
+          from: 0
+          to: 1
+          stepSize: 0.01
+          value: Settings.data.dock.backgroundOpacity
+          onMoved: Settings.data.dock.backgroundOpacity = value
+          cutoutColor: Color.mSurface
+        }
+
+        NText {
+          text: Math.floor(Settings.data.dock.backgroundOpacity * 100) + "%"
+          Layout.alignment: Qt.AlignVCenter
+          Layout.leftMargin: Style.marginS * scaling
+          color: Color.mOnSurface
+        }
+      }
+    }
+
     ColumnLayout {
       spacing: Style.marginXXS * scaling
       Layout.fillWidth: true