Examine source code of https://addons.org

{
  "name": "123456",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "Screenshot_2018-12-30-05-15-52-566_Firefox.png"
    },
    "colors": {
      "toolbar": "rgba(76, 22, 135, 1)",
      "toolbar_field": "rgba(111, 32, 196, 1)",
      "toolbar_field_text": "rgba(28, 132, 230, 1)",
      "frame": "rgba(62, 37, 71, 1)",
      "tab_background_text": "rgba(37, 130, 184, 1)",
      "bookmark_text": "rgba(45, 55, 204, 1)"
    }
  }
}