I already wrote it as "margin-left" and "margin-right". And also I set width as 100% in one version and in pixels in another version.
 
I am still looking for a solution...

From: Alessandro Antonello <antonello.ale@gmail.com>
To: openguen <openguen@yahoo.co.uk>; Inkscape User Community <inkscape-user@lists.sourceforge.net>
Sent: Sunday, 2 October 2011, 6:29
Subject: Re: [Inkscape-user] align the web page centerally

2011/10/1 openguen <openguen@yahoo.co.uk>:
> Unfortunately, no change occured; and also it didn't yield any error.
>
>
> If you're not using a separate *.css file, try putting it in the <svg> tag:
>
> <svg style="left-margin: auto; right-margin: auto;"
>

Shouldn't it be 'margin-left' and 'margin-right'? Since it is CSS, the
'margin' thing should come first. You must set 'width' also so the margins are
really automatically defined.