Examine source code of Concrete Theme

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Concrete Theme",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(230, 230, 230)",
      "toolbar_text": "rgb(0, 0, 0)",
      "frame": "rgb(170, 170, 170)",
      "tab_background_text": "rgb(0, 0, 0)",
      "toolbar_field": "rgb(255, 255, 255)",
      "toolbar_field_text": "rgb(0, 0, 0)",
      "tab_line": "rgba(230, 230, 230, 0)",
      "popup": "rgb(230, 230, 230)",
      "popup_text": "rgb(0, 0, 0)",
      "tab_loading": "rgba(230, 230, 230, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8a474b1a-6cf8-481d-8413-ed102d83abd8}"
    }
  }
}