Removing the whitespace above a scatter plot [newbie]

Thanks so much for this wonderful tool. I was able to quickly build my first effort - a scatter plot.

The one bit I'm still trying to figure out is how to remove the whitespace at the top. I'm guessing it's something to do with the "header" object?

Here's my spec:

{
  "data": {"name": "dataset"},
  "mark": {
    "type": "point",
    "filled": true,
    "size": 20,
    "color": "#444444",
    "tooltip": true
  },
  "encoding": {
    "x": {
      "field": "Report Date_1",
      "type": "temporal",
      "title": null
    },
    "y": {
      "field": "Random 1",
      "type": "quantitative",
      "axis": null
    }
  }
}

In this screenshot, the green bar is the standard Power BI Title, which I'd prefer to leave in place. There's a lot of whitespace at the top, between the Power BI title and the top of the scatter plot. The whitespace at the left and right and bottom looks reasonable to me.

deneb-viz / deneb-viz.github.io

Removing the whitespace above a scatter plot [newbie] #29