Copy and paste a message for Slack

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Copy and paste a message for Slack",
  "short_name": "copipesl",
  "version": "1.1.0",
  "manifest_version": 2,
  "description": "Copy a message and paste it into textarea.",
  "icons": {
    "16": "icons/icons8-Slack-64.png",
    "48": "icons/icons8-Slack-64.png",
    "128": "icons/icons8-Slack-64.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.slack.com/*"
      ],
      "js": [
        "jquery-3.2.1.min.js",
        "content-script.js"
      ],
      "css": [
        "content-style.css"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "<all_urls>"
  ]
}