updating styles to use theme colours

styles/CwtchTextAreaStyle.qml

@@ -1,8 +1,8 @@
 import QtQuick.Controls.Styles 1.4
 import QtQuick 2.7
-
+import "theme"
 
 TextAreaStyle {
     textColor: "black"
-    backgroundColor: windowItem.cwtch_background_color
+    backgroundColor: Theme.backgroundPaneColor
 }