src/Pure/GUI/gui.scala

--- a/src/Pure/GUI/gui.scala	Sat Nov 02 20:27:41 2024 +0100
+++ b/src/Pure/GUI/gui.scala	Sun Nov 03 14:11:01 2024 +0100
@@ -49,6 +49,10 @@
         .filterNot(info => old_lafs(info.getClassName))
     val more_lafs = look_and_feels.map(_.info)
     UIManager.setInstalledLookAndFeels((more_lafs ::: lafs).toArray)
+
+    // see https://www.formdev.com/flatlaf/customizing
+    UIManager.put("Component.arrowType", "triangle")
+    UIManager.put("ScrollBar.showButtons", true)
   }
 
 
@@ -266,6 +270,11 @@
       tree.getSelectionModel.setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION)
     }
 
+    // follow jEdit
+    if (!GUI.is_macos_laf) {
+      tree.putClientProperty("JTree.lineStyle", "Angled")
+    }
+
     tree
   }