{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "style": {
    "font-size": "20px",
    "white-space": "nowrap"
  },
  "attributes": {
    "class": "ms-fontColor-themePrimary"
  },
  "children": [
    {
      "elmType": "span",
      "txtContent": "=padStart('' , @currentField , '▮')"
    },
    {
      "elmType": "span",
      "txtContent": "=padStart('' , 5 - @currentField , '▯')"
    }
  ]
}