Examine source code of adwaita

{
  "name": "adwaita",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "hit0.png"
    },
    "colors": {
      "frame": "rgba(30, 30, 30, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(48, 48, 48, 1)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(68, 68, 68, 1)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9381eade-1aea-4d54-9c48-3c94aaeddfef}"
    }
  }
}