Examine source code of Debug CSS

{
  "manifest_version": 2,
  "name": "Debug CSS",
  "short_name": "Debug CSS by Pranay Joshi",
  "description": "Adds outline to all elements on the page to show the culprit element which is changing desired layout",
  "version": "1.1resigned1",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "debug-CSS.js"
    ]
  },
  "browser_action": {
    "default_title": "Toggle Debug CSS",
    "default_icon": {
      "19": "images/toolbar-chrome.png",
      "38": "images/toolbar-chrome@2x.png"
    }
  },
  "commands": {
    "toggle-pin": {
      "suggested_key": {
        "default": "Alt+Shift+C"
      },
      "description": "Toggle Debug CSS"
    }
  },
  "icons": {
    "16": "icon_16.png",
    "48": "icon_48.png",
    "128": "icon_128.png"
  },
  "web_accessible_resources": [
    "debugCSS.min.css",
    "debugCSS.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b7303beb-09e0-48e1-88bc-0de02b7b60ef}"
    }
  }
}