Exit-Intent Thank-You Pop-Up

I need a clean, lightweight pop-up that appears only when a visitor shows exit intent—moving the cursor toward the browser’s close button or navigating away. Its sole purpose is to display a warm “Thank you for visiting” message; no email capture, promos, or redirects.

Here’s what I’m expecting:
• A self-contained HTML/CSS/JavaScript snippet (vanilla JS or a tiny jQuery block is fine) that I can drop into any page.
• Smooth, non-intrusive animation with a close (“×”) icon.
• Responsive styling so it looks good on desktop, tablet, and mobile.
• A quick read-me explaining where to place the code and how to tweak colors, fonts, and the message copy.

The script must fire reliably on all major browsers without slowing the page down. If you have a preferred lightweight exit-intent library, feel free to use it as long as you keep external dependencies minimal and open-source.

Please send a short demo link or GIF along with the code so I can preview the behavior before final hand-off.