Update: Improve drag handle styling by using GNOME Settings style

This also finally makes the style `<class name="drag-handle"/>` in
`prefs-box-order-item-row.ui` actually do something.

data/css/prefs.css

@@ -0,0 +1,9 @@
+/* Taken from: https://gitlab.gnome.org/GNOME/gnome-control-center/-/blob/43.5/shell/style.css */
+
+.drag-handle {
+  color: alpha(@theme_fg_color, 0.4);
+}
+
+.drag-handle:backdrop {
+  color: alpha(@theme_unfocused_fg_color, 0.4);
+}

package.sh

@@ -9,4 +9,5 @@ gnome-extensions pack "$REAL_BASE_DIR/src" \
     --extra-source extensionModules \
     --extra-source prefsModules \
     --extra-source ../data/ui \
+    --extra-source ../data/css \
     --schema ../data/org.gnome.shell.extensions.top-bar-organizer.gschema.xml

src/prefs.js

@@ -1,11 +1,22 @@
 "use strict";
 /* exported buildPrefsWidget, init */
 
+const Gtk = imports.gi.Gtk;
+const Gdk = imports.gi.Gdk;
+
 const ExtensionUtils = imports.misc.extensionUtils;
 const Me = ExtensionUtils.getCurrentExtension();
 
 const PrefsPage = Me.imports.prefsModules.PrefsPage;
 
+const provider = new Gtk.CssProvider();
+provider.load_from_path(Me.dir.get_path() + "/css/prefs.css");
+Gtk.StyleContext.add_provider_for_display(
+    Gdk.Display.get_default(),
+    provider,
+    Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION
+);
+
 function buildPrefsWidget() {
     return new PrefsPage.PrefsPage();
 }