how to position absolute div element over a fixed div elemen

here's the link:

http://license.relatebase.com/cl/dc/console/login/temp258.php

start typing in the text area "Abstract" - then click the ^ button to the right. OK, that's pretty obvious; when you tab out, the contents goes back into the original text area.

Waht's not obvious to me are two things (by priority):
1. how do I position the floating and larger textarea over the text area below, upper left corners meeting together?
2. the big div set to opacity=50% - I set it to width=height=100%, but it doesn't cover the hidden part of the viewport, only the initially seen part; any way to fix.

Thank you for help over the years!

Sam