jQuery is a great library which greatly simplifies and improves the whole Javascript workflow for web developers.
After hours of punching CSS, you may think of cutting-the-head-of-the-bull (Italian proverb) and go for jQuery to adjust that f*****g div.
$(".textarea").css("height"),$(window).height()-50);
There you go, the -50 are pixels and it's needed to actually prevent the div to spread to the whole browser window!