Colors: slight rework of the default colorscheme and overall colors usage

Widgets/NBox.qml

@@ -11,7 +11,7 @@ Rectangle {
   implicitWidth: childrenRect.width
   implicitHeight: childrenRect.height
 
-  color: Colors.surfaceVariant
+  color: Colors.surface
   radius: Style.radiusMedium * scaling
   border.color: Colors.backgroundTertiary
   border.width: Math.max(1, Style.borderThin * scaling)

Widgets/NCircleStat.qml

@@ -57,8 +57,8 @@ Rectangle {
           const endBg = Math.PI * 5 / 3
           ctx.reset()
           ctx.lineWidth = 6 * root.scaling * contentScale
-          // Track uses backgroundPrimary for stronger contrast
-          ctx.strokeStyle = Colors.backgroundPrimary
+          // Track uses surfaceVariant for stronger contrast
+          ctx.strokeStyle = Colors.surfaceVariant
           ctx.beginPath()
           ctx.arc(cx, cy, r, start, endBg)
           ctx.stroke()
@@ -89,7 +89,7 @@ Rectangle {
         width: 28 * scaling * contentScale
         height: width
         radius: width / 2
-        color: Colors.backgroundSecondary
+        color: Colors.surfaceVariant
         // border.color: Colors.accentPrimary
         // border.width: Math.max(1, Style.borderThin * scaling)
         anchors.right: parent.right

Widgets/NTooltip.qml

@@ -138,11 +138,11 @@ Window {
     gradient: Gradient {
       GradientStop {
         position: 0.0
-        color: Colors.backgroundTertiary
+        color: Colors.backgroundSecondary
       }
       GradientStop {
         position: 1.0
-        color: Colors.backgroundSecondary
+        color: Colors.backgroundTertiary
       }
     }
     border.color: Colors.outline