Examine source code of U2....

{
  "theme": {
    "images": {
      "theme_frame": "u21.jpg"
    },
    "colors": {
      "frame": "#210c0c",
      "tab_background_text": "#210c0c"
    }
  },
  "version": "2.0",
  "name": "U2....",
  "manifest_version": 2
}