How to center the label on the screen?

Question

I'm specifing the size of the windows within the window.open(), but regardless of the size, I would like this label to be exactly on the center of the screen (vertically and horizontally):

<?xml version="1.0" encoding="UTF-8"?>

<window sizemode="maximized" hidechrome="true" id="weatherWindow" title="Window"
    xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"&gt;

    <label style="background:#FFFF00; margin: auto auto auto auto; text-align:center;">LOADING...</label>

</window>

The text is centered horizontally only, any idea how to center it vertically either?

Answer 1

See this article for centering something vertically on the screen using CSS.

Answer 2

Without touching CSS, you can put it in a vbox and set pack="center" on the vbox.