Examine source code of Default dark

{
  "theme": {
    "images": {
      "theme_frame": "myfirebar.jpg"
    },
    "colors": {
      "frame": "#f5860e",
      "tab_background_text": "#fafafa"
    }
  },
  "version": "2.0",
  "name": "Default dark",
  "manifest_version": 2
}