mapcomplete/assets/layers/range/range.json

{
  "id": "range",
  "description": "Meta-layer, simply showing a bbox in red",
  "title": null,
  "source": "special",
  "name": null,
  "shownByDefault": false,
  "mapRendering": [
    {
      "width": 3,
      "fill": "no",
      "color": "#cc00cc"
    }
  ]
}