Hidden commands in HTML

HTML

<!DOCTYPE html>
<html>
<body>
	<p>
		echo "I'm just some friendly command"<br>
		<span style="color:white;font-size:0pt;">echo "Haha, you've just run a bad command. Your system is rekt now."<br></span>
		echo "Copy and run me."
	</p>
</body>
</html>