Examine source code of Adwaita-dark

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Adwaita-dark",
  "browser_specific_settings": {
    "gecko": {
      "id": "adwaita-dark@minoru.com"
    }
  },
  "description": "This color scheme blends well with the Adwaita GTK theme.",
  "theme": {
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(69, 69, 69)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(53, 53, 53)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(53, 53, 53)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(69, 69, 69)",
      "popup": "rgb(53, 53, 53)",
      "popup_text": "rgb(255, 255, 255)",
      "icons_attention": "rgb(27, 106, 203)",
      "toolbar_field_border_focus": "rgb(27, 106, 203)",
      "tab_loading": "rgb(69, 69, 69)"
    }
  }
}