Examine source code of Owl - Dark Background

{
  "name": "Owl - For comfortable reading",
  "short_name": "Owl",
  "description": "An add-on to make online reading easy.\nIf you spend long hours in front of a computer screen, you likely have developed an aversion towards those glaring white backgrounds and harsh color combinations on websites.\nThis add-on transforms all webpages into a night-friendly mode, with dark background and dimmed colors.",
  "version": "2.2.8",
  "homepage_url": "http://owl.sidhant.io/",
  "icons": {
    "48": "data/icons/enabled-48.png",
    "64": "data/icons/enabled-64.png",
    "96": "data/icons/enabled-96.png"
  },
  "permissions": [
    "*://*/*",
    "storage",
    "activeTab",
    "tabs"
  ],
  "applications": {
    "gecko": {
      "id": "@owl-comfortable-reading-addon",
      "strict_min_version": "46.0"
    }
  },
  "browser_action": {
    "browser_style": false,
    "default_title": "Owl button",
    "default_icon": {
      "16": "data/icons/enabled-16.png",
      "32": "data/icons/enabled-32.png",
      "64": "data/icons/enabled-64.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "page_action": {
    "default_icon": {
      "16": "data/icons/enabled-16.png",
      "32": "data/icons/enabled-32.png",
      "64": "data/icons/enabled-64.png"
    },
    "default_title": "Open Owl Panel",
    "default_popup": "data/markup/panel.html",
    "browser_style": false
  },
  "options_ui": {
    "browser_style": true,
    "page": "data/markup/owl_preferences.html",
    "open_in_tab": false
  },
  "commands": {
    "toggle-owl": {
      "suggested_key": {
        "default": "Alt+Shift+D"
      },
      "description": "Toggle Own ON or OFF"
    },
    "toggle-classic": {
      "suggested_key": {
        "default": "Alt+Shift+C"
      },
      "description": "Use classic theme on current page"
    },
    "toggle-current-site": {
      "suggested_key": {
        "default": "Alt+Shift+X"
      },
      "description": "Enable/Disable Owl on current website"
    }
  },
  "developer": {
    "name": "Sidhant Sharma [:tk]",
    "url": "http://sidhant.io"
  },
  "manifest_version": 2
}