Don't nest all content in background rect

This way we don't have an extra identation depth, makes it a bit easier to read

CURA-8726

plugins/Marketplace/resources/qml/Marketplace.qml

@@ -46,7 +46,7 @@ Window
     {
         anchors.fill: parent
         color: UM.Theme.getColor("main_background")
-
+    }
     //The Marketplace can have a page in front of everything with package details. The stack view controls its visibility.
     StackView
     {
@@ -64,8 +64,8 @@ Window
             // Page title.
             Item
             {
-                    Layout.preferredWidth: parent.width
-                    Layout.preferredHeight: childrenRect.height + UM.Theme.getSize("default_margin").height
+                implicitWidth: parent.width
+                implicitHeight: childrenRect.height + UM.Theme.getSize("default_margin").height
 
                 Label
                 {
@@ -241,7 +241,6 @@ Window
             }
         }
     }
-    }
 
     Rectangle
     {