{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "background": "white",
  "padding": 5,
  "width": 20,
  "height": 20,
  "data": [{"name": "source_0", "values": [{"a": 2}]}],
  "marks": [
    {
      "name": "marks",
      "type": "symbol",
      "style": ["point"],
      "from": {"data": "source_0"},
      "encode": {
        "update": {
          "opacity": {"value": 0.7},
          "fill": {"value": "transparent"},
          "stroke": {"value": "purple"},
          "ariaRoleDescription": {"value": "point"},
          "x": {"signal": "width", "mult": 0.5},
          "y": {"signal": "height", "mult": 0.5}
        }
      }
    }
  ]
}