Sorry pushed enter too soon. I can make the problem go away by changing the line in mate-panel.rc from
class "GtkScrollbar" style "murrine-scrollbar"
to
class "GtkScrollbar" style "scrollbar"
which is what is shown e.g. here
https://github.com/lemonsqueeze/Ambiant-MATE-Orange/blob/master/gtk-2.0/apps/mate-panel.rc
Sorry pushed enter too soon. I can make the problem go away by changing the line in mate-panel.rc from
class "GtkScrollbar" style "murrine-scrollbar"
to
class "GtkScrollbar" style "scrollbar"
which is what is shown e.g. here
https:/ /github. com/lemonsqueez e/Ambiant- MATE-Orange/ blob/master/ gtk-2.0/ apps/mate- panel.rc