Examine source code of Proton Mail (Proton)

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "Proton Mail",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(61, 43, 144)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(27, 19, 64)",
      "tab_background_text": "rgb(146, 130, 212)",
      "toolbar_field": "rgb(42, 29, 101)",
      "toolbar_field_text": "rgb(222, 215, 255)",
      "tab_line": "rgb(124, 92, 255)",
      "popup": "rgb(247, 245, 255)",
      "popup_text": "rgb(55, 55, 56)",
      "button_background_active": "rgb(46, 34, 95)",
      "button_background_hover": "rgb(41, 29, 88)",
      "icons_attention": "rgb(247, 132, 1)",
      "icons": "rgb(255, 255, 255)",
      "ntp_background": "rgb(247, 245, 255)",
      "popup_border": "rgb(209, 207, 205)",
      "tab_loading": "rgb(124, 92, 255)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{39cee380-a030-44b9-9777-0d1fe3b79a33}"
    }
  }
}