Lxappearance is used to set all elements concerning OPENBOX.
You can set the theme (called Widget here), the icon theme and the mouse cursor (will add folder ‘default’ in ~/.icons).
Separately from the theme you can set also the window decorations (bar at the top) in Window Border and that is a bit confusing depending on what distro you are used to work on.
To make it even more confusing the window border will ALSO SET THE MENU OF OPENBOX. So right-mouse click on the desktop.
You have a lot of choices for both the Widget and the Window border.
We have created many versions of the Arc theme with different colors next to the standard blue and so you can also select Arc theme version for your Window Border.
But there are many more versions of Window Borders you can apply.
Lxappearance will NOT set thunar the filemanager. Thunar is part from xfce and will be set with xfce appearance.