Examine source code of Hide LeetCode Difficulty

{
  "manifest_version": 2,
  "name": "Leetcode Difficulty Hider",
  "version": "1.1",
  "description": "Hides LeetCode problem difficulty.",
  "permissions": [],
  "icons": {
    "128": "icons/leetcode_difficulty_hider_128_128.jpeg"
  },
  "content_scripts": [
    {
      "matches": [
        "*://leetcode.com/problems/*",
        "*://leetcode.com/problemset/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_end"
    }
  ],
  "applications": {
    "gecko": {
      "id": "difficulty-hider@example.com"
    }
  }
}