Can't make text-area resizable to fit windows size

I am trying to make a text-area resizable with this code:

<div class="fields" style="resize:both;">
  <div class="text-area-display-panel" style="resize:both;">
    ...contents...
  </div>
</div>

However, it's not working, and I can't find out why (it should be that simple, right?). Besides, is there any CSS property or similar to make the window always fit the window size?

Thanks a lot.