Examine source code of Dark Theme for Firefox

{
  "manifest_version": 2,
  "version": "2.0",
  "name": "Dark Theme",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-029-cc9cab928c1799136d18758709e91ecc.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(33, 33, 33)",
      "toolbar_field": "rgb(56, 56, 54)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(151, 100, 218)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(46, 46, 62)",
      "tab_loading": "rgb(151, 100, 218)",
      "bookmark_text": "rgb(218, 218, 218)",
      "frame": "rgb(56, 56, 52)",
      "tab_background_text": "rgb(124, 124, 126)"
    }
  }
}