Examine source code of idk...

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "idk",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-001-9c6d74e14860e77ee6f8f43e824bff25.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(36, 124, 122)",
      "toolbar_text": "rgb(207, 212, 140)",
      "frame": "rgb(148, 182, 86)",
      "tab_background_text": "rgb(19, 91, 88)",
      "toolbar_field": "rgb(90, 90, 63)",
      "toolbar_field_text": "rgb(105, 207, 160)",
      "tab_line": "rgb(137, 198, 25)",
      "popup": "rgb(90, 90, 63)",
      "popup_text": "rgb(207, 212, 140)",
      "tab_loading": "rgb(137, 198, 25)"
    }
  }
}