Examine source code of Black-gray gradient

{
  "name": "Black-gray gradient",
  "manifest_version": 2,
  "version": "3.0",
  "theme": {
    "images": {
      "theme_frame": "black.png"
    },
    "colors": {
      "toolbar": "rgba(0, 0, 0, 0.95)",
      "toolbar_field": "rgba(71, 71, 71, 1)",
      "toolbar_field_text": "rgba(240, 240, 240, 1)",
      "frame": "rgba(229, 230, 232, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "bookmark_text": "rgba(168, 168, 168, 1)"
    }
  }
}