Graphene graphql dictionary as type

Question

I am new to grapgene and I am trying to map the following structure to an object type and have not succeeded at all

    {
  "details": {
    "12345": {
      "txt1": "9",
      "txt2": "0"
    },
    "76788": {
      "txt1": "6",
      "txt2": "7"
    }
  }
}

Any guidance is much appreciated.
Thanks