SlackBuildsOrg/desktop/yad

Yad displays graphical dialogs from shell scripts or command line.

Yad is a fork of Zenity with many improvements, including custom
buttons, additional dialogs and a pop-up menu in the notification
area.

The optional dependency webkitgtk enables the html widget.

By default this is built against gtk+2: if you want to use it
with gtk+3 pass the script the parameter GTK=3