Examine source code of nature_

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "nature_1",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right bottom"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(0, 0, 0, 0)",
      "toolbar_text": "rgb(74, 167, 23)",
      "frame": "rgb(70, 70, 70)",
      "tab_background_text": "rgb(225, 225, 225)",
      "toolbar_field": "rgba(255, 255, 255, 0.1)",
      "toolbar_field_text": "rgb(202, 202, 202)",
      "tab_line": "rgb(202, 202, 202)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(0, 0, 0)",
      "tab_loading": "rgb(202, 202, 202)"
    }
  }
}