To be used on https://adventofcode.com/XXXX/stats page

percent.js

var stats = document.getElementsByClassName('stats-both');
var firstOnlyStats = document.getElementsByClassName('stats-firstonly');
var total = parseInt(stats[stats.length-2].textContent, 10) + parseInt(firstOnlyStats[firstOnlyStats.length-2].textContent, 10);
for (var i = 0; i < stats.length; i++)
{
	var num = parseInt(stats[i].textContent, 10);
	var numBoth = parseInt(firstOnlyStats[i].textContent, 10) + num;
	if (!isNaN(num))
	{
		var percent = ""+Math.round(num*100/total);
		var percentBoth = ""+Math.round(numBoth*100/total)
		percent = `(${percent.padStart(2, ' ')}%)`;
		percentBoth = `(${percentBoth.padStart(3, ' ')}%)`;
		if (num === 0)
			percent = "".padStart(5, ' ');
		if (numBoth === 0)
			percentBoth = "".padStart(5, ' ');
		stats[i].textContent = `${stats[i].textContent} ${percent}`;
		firstOnlyStats[i].textContent = `${firstOnlyStats[i].textContent} ${percentBoth}`;
	}
}