Panel - Vertical - Stretch Fill

          $(go.Node, 'Auto',
            { width: 200, height: 200 },
            $(go.Shape, "RoundedRectangle", {
              fill: 'blue',
              stretch : go.GraphObject.Fill,
            $(go.Panel, 'Vertical',
              { stretch: go.GraphObject.Fill },
              $(go.TextBlock, 'Hallo', { background: 'white', textAlign: 'center' }),
              $(go.Shape, 'RoundedRectangle', { stretch: go.GraphObject.Fill, fill: 'yellow' })

Hello, why is the yellow Shape not stretch “fill”?

Thank you for help.

Vertical panels don’t stretch their elements in the vertical direction, only horizontally. See the first paragraph in the intro on Vertical panels.

You may want to use a Table panel instead.