class SPTestView : View("SPTest") {
    override val root = stackpane {
        text("I want to be centered")
    }
}
class SPTestApp : App(SPTestView::class) {

    override fun start(stage: Stage) {
        stage.minWidth = 1024.0
        stage.minHeight = 768.0
        super.start(stage)  // move up 3 lines to center
    }
}