Help me centering the objects/elements.

Ok so I’m trying to make a responsive theme. But I have a problem with centering the objects within <div id=”post-detail”>. But centering the things within <div id=”sharethis” > and <div id=”long-desc” > when the screen is less than 611px wide wasn’t any problem when I added this code to my style.css:

@media screen and (max-width: 611px) {

#content-post{
max-width:970px;
width: 100%;
float:left;
height:auto;
padding-top:15px;
margin: 0px auto;
text-align: center;
}
}

You can check out the site here: http://alphasurvivalgear.com/alphacore-survival-kit/

Image of the problem: http://i.imgur.com/zBWGgqP.png

Please help me centering the objects within <div id=”post-detail”>.

Thank you,

Taskemann