{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "children": [
    {
      "elmType": "span",
      "style": {
        "width": "14px",
        "height": "14px",
        "border-radius": "50%"
      },
      "attributes": {
        "class": "=if(@currentField == 'Green', 'ms-bgColor-green', if(@currentField == 'Yellow', 'ms-bgColor-yellow', if(@currentField == 'Red', 'ms-bgColor-red', '')))"
      }
    }
  ]
}