I looked at your CSS. This is what can be causing it:
Code:
div#root table#root_table {
margin-left: auto;
margin-right: auto;
}
Try getting rid of it and see if that changes it. The default is left align, so the only place I can think of that somebody could change it is CSS. I could be wrong though lol.
If you want to just center some things, I would just stick them between DIV tags if html, or Align tags if BBCode.
Code:
<DIV align="center"> whatever you want centered in here</DIV>
or
Code:
[align=center]whatever you want centered in here[align]
I would suggest to keep css clean because there are some things you don't really need in there that can be easily controlled through the console that they have just to keep it manageable for yourself. For example I used the Theme Configuration to size my columns. You can also change the alignment of your site (not the text hehe) here as well. It's there...less coding for us!
If you feel adventurous and want to really mould your site into something different, then check out this post
viewtopic.php?f=5&t=4359 on some CSS tags.
Otherwise, if you aren't deviating too far from the original template, then keep it simple. I'm not the biggest fan of coding, so I use what I can of the console, then use CSS

, which I only have about 4 or 5 selectors manipulated.