Examine source code of Linux Mint Dark

{
  "name": "Linux Mint Dark",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "firefox titlebar.png"
    },
    "colors": {
      "frame": "rgba(46, 46, 46, 1)",
      "tab_background_text": "rgba(120, 120, 120, 1)",
      "toolbar": "rgba(53, 53, 53, 1)",
      "bookmark_text": "rgba(240, 240, 240, 1)",
      "toolbar_field": "rgba(46, 46, 46, 1)",
      "toolbar_field_text": "rgba(240, 240, 240, 1)"
    }
  }
}