Examine source code of Grey-dient

{
  "theme": {
    "images": {
      "theme_frame": "firefox_header.png"
    },
    "colors": {
      "frame": "#cccccc",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Grey-dient",
  "manifest_version": 2,
  "description": "Simple gradient with white at the top going to grey at the bottom. Works best with the default Linux skin."
}