Examine source code of dark

{
  "name": "dark",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "3.png"
    },
    "colors": {
      "frame": "rgba(17, 17, 17, 1)",
      "tab_background_text": "rgba(68, 68, 68, 1)",
      "toolbar": "rgba(25, 25, 25, 1)",
      "bookmark_text": "rgba(238, 238, 238, 1)",
      "toolbar_field": "rgba(17, 17, 17, 1)",
      "toolbar_field_text": "rgba(238, 238, 238, 1)",
      "tab_line": "rgba(0, 0, 0, 0.1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ff79b90f-d387-4c10-b06a-6a69e60c632c}"
    }
  }
}