Download Extension from Chrome Web Store:

https://chrome.google.com/webstore/detail/squarespace-ninja-kit-ext/klkcninekpnpemndealaeebjajmkabcf

Step 1 - Open Code Injection

In the Home Menu, click Settings, click Advanced, and then click Code Injection.

Step 2 - Add HTML code

Add below scripts into the appropriate Code Injection fields for the headerfooter

Header

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.11.2/css/all.css"  />
<link rel="stylesheet" href="https://ninjakit-assets.ixstudio.net/assets/admin/css/ninja-sqs.css" />
<script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]"></script>

Footer

<script src="https://ninjakit-assets.ixstudio.net/assets/admin/js/ninja-sqs.js"></script>

Step 3 - Save

After adding your code, click Save.

That's all! Enjoy it 🙂