Kvision panel should take up 100 percent height?

Question

I'm using kvision to build a web client that should show show a table of items, using a tabulator. How do I create a panel for my tabulator, if I want it to fill the whole browser window. Here is a simpler example:

root {
  add(FullScreenPanel())
}

class FullScreen : SimplePanel() {
    init {
        height = 100.perc
        width = 100.perc
        background = Background(Color.name(Col.RED))
        b("Hello world!")
    }
}

It stretches the full width, but the height is only the height of the b("Hello world") object.