Gtk.Button.prototype.set_alignment

function set_alignment(xalign:Number, yalign:Number):void {
    // Gjs wrapper for gtk_button_set_alignment()
}

Sets the alignment of the child. This property has no effect unless the child is a Gtk.Misc or a Gtk.Alignment.

Since 2.4

xalign

the horizontal position of the child, 0.0 is left aligned, 1.0 is right aligned

yalign

the vertical position of the child, 0.0 is top aligned, 1.0 is bottom aligned