Examine source code of Nocturnal

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#1d1e2a",
      "tab_background_text": "#d4d4d4"
    }
  },
  "version": "2.0",
  "name": "Nocturnal",
  "manifest_version": 2,
  "description": "Nocturnal Firefox theme to match the Nocturnal Visual Style."
}