To use the overlay install the following browser extension
USE THIS FOR CHROME
https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldmpobfkfo?hl=en

FOR OPERA YOU WILL NEED TO FIND IT FROM THE SITE
https://www.tampermonkey.net/

USE THIS FOR FIREFOX
https://addons.mozilla.org/en-US/firefox/addon/violentmonkey/

Then paste this script https://github.com/italyplace/thing/raw/main/userscript.user.js

A nice and simple 2-click solution to making sure you never place an incorrect pixel!