Position on screen of dhtmlx.message

Spreadsheet
#1

The following code displays the message top left of the screen in IE9, and top right of the screen in Firefox.
Putting at the top of the code, moves it to top right for both browsers.
(This is using the latest files downloaded from github)

I would really like it in the center of the screen for both browsers. How can I achieve this?
TIA

[code]

<link rel="stylesheet" type="text/css" href="./dhtmlx.css">
<link rel="stylesheet" type="text/css" href="./message/codebase/themes/message_default.css">
[/code]
#2

Add style like next on the page

.dhtmlx_message_area{ left:50%; margin-left:-125px; }