I'm trying to popup a login dialog over a page. I want the page to be slightly occluded by a semi-transparent layer.

So I got that to work (huzzah!), but if the user scrolls, the semi-transparent layer (called cloak) only covers part of the page (it's got a top and left of 0 in the CSS), and it only goes down as far as the size of the browser window.

I used X to set the size of the cloak div to that of document.body. That worked in width, but in height it was short by about 70px. Not sure why... This is in FF

I added 70px, and it worked, covering the page to the bottom. If someone can explain why it came up short, I'd appreciate it.

The next item is positioning the dialog box in the current viewport. It may also be desirable to make it travel as the user scrolls. Can someone point me to the right functions in XLib for that?