Examine source code of Black Gradient

{
  "theme": {
    "images": {
      "theme_frame": "Header.png"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#cfcfcf"
    }
  },
  "version": "2.0",
  "name": "Black Gradient",
  "manifest_version": 2,
  "description": "A simple black-to-grey gradient"
}