Thanks for your numbered comments.
I have confused this library with the newer cross-platform. (
SD_TreeList)
I'll answer your comments.
1st Changing the properties to MenuTree1.GetBase will have no effect because there are other views that cover the base, the ones that make up the tree.
2nd It is not foreseen, therefore it is not possible, to change the bottom of the views that form the tree.
3rd This library is unlikely to be updated which is now over three years old and an XUI version exists. multi-platform.
4th You can change the background color only with the Background property of the design. But I don't think this is what you are looking for. (In this example I have changed the background to red)
View attachment 101377
5th I hope I have answered your questions
6th Best regards