Examine source code of ProtonMail

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "ProtonMail",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-037-b73f9b34467ba541de861f5b4c0c6316.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(49, 53, 61)",
      "toolbar_text": "rgb(246, 247, 250)",
      "frame": "rgb(38, 42, 51)",
      "tab_background_text": "rgb(215, 226, 239)",
      "toolbar_field": "rgb(27, 29, 36)",
      "toolbar_field_text": "rgb(246, 247, 250)",
      "tab_line": "rgb(101, 126, 228)",
      "popup": "rgb(46, 50, 61)",
      "popup_text": "rgb(246, 247, 250)",
      "tab_loading": "rgb(101, 126, 228)"
    }
  }
}