I tried to use the Macbuntu theme using the Ubuntu Tweak tool, and all it does is change the appearance inside the windows of apps such as System Settings. The window borders, buttons for close/minimize/maximize, and the fonts remain the same (default), and also everything inside nautilus remains the same. I was able to change the icon theme and the cursor theme using the tweak tool, though.
I even tried using one of the default themes from System Settings>Appearance, and again, only the contents of the window changes, while the taskbar and window borders remain the same, and the whole of nautilus remains unchanged.
Any ideas as to why this is happening? Thanks!