The settings dialog can be either invoked via the application menu or the commandline: xfce4-notifyd-config.

It allows you to configure the following settings.

When set to Default the osd and app-notification style classes of your currently selected Gtk+3 theme will be used.

When set to a different theme-name, it will use the respective standalone Xfce4-notifyd theme.

This setting determines where on your screen notifications will show up by default.

This timeout determines how long notifications will be shown until they gracefully fade out. If a notification is designed to be persistent, this value will not apply (e.g. warnings related to low battery power).

This setting allows you to set a default opacity for notifications. This only works when using a compositing window manager.

This shows a sample notification based on the style you have selected in the options described above.