Examine source code of Old School Steam

{
  "manifest_version": 2,
  "version": "2.0",
  "name": "Old School Steam",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(76, 88, 68)",
      "toolbar_text": "rgb(188, 199, 177)",
      "frame": "rgb(76, 88, 68)",
      "tab_background_text": "rgb(245, 245, 245)",
      "toolbar_field": "rgb(62, 70, 55)",
      "toolbar_field_text": "rgb(201, 196, 140)",
      "tab_line": "rgb(201, 196, 140)",
      "popup": "rgb(88, 106, 80)",
      "popup_text": "rgb(255, 255, 255)",
      "button_background_active": "rgb(62, 70, 55)",
      "ntp_background": "rgb(62, 70, 55)",
      "ntp_text": "rgb(188, 199, 177)",
      "popup_border": "rgb(117, 116, 122)",
      "sidebar_border": "rgb(201, 196, 140)",
      "sidebar_highlight_text": "rgb(255, 255, 255)",
      "sidebar_highlight": "rgb(40, 46, 32)",
      "sidebar_text": "rgb(188, 199, 177)",
      "sidebar": "rgb(63, 70, 55)",
      "tab_selected": "rgb(62, 70, 55)",
      "tab_text": "rgb(201, 196, 140)",
      "toolbar_bottom_separator": "rgb(47, 49, 39)",
      "toolbar_top_separator": "rgb(135, 144, 125)",
      "tab_loading": "rgb(201, 196, 140)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{26135e2d-7c3b-4f87-bdf2-d97050def6ff}"
    }
  }
}