10-trackball.conf

# File: /usr/share/X11/xorg.conf.d/10-trackball.conf

Section "InputClass"
    Identifier "Marble Mouse"
    MatchProduct "Logitech USB Trackball"
    Driver "libinput"
    Option "ScrollMethod" "button"
    # Button "9" is the little button on the /right/ side of the
    # mouse.
    #
    # Most right-handed people will probably want to use "8", which is
    # the little button on the /left/ side of the mouse.
    Option "ScrollButton" "9"
    Option "MiddleEmulation" "on"
EndSection