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