de-net/src/entry/content.js

console.log('123 world content todo something~')
addDeNetBtn();

function addDeNetBtn () {
	let scheduleTweet = document.querySelectorAll('[aria-label="Schedule Tweet"]')[0];
	let span = document.createElement('span');
	span.innerText = 'test';
	scheduleTweet.parentNode.insertBefore(span, scheduleTweet.nextSibling);
	console.log(scheduleTweet)
}