Center Positioning of Logo in pp_newswire

My CSS skills are rusty, but I'm at a loss as to how to center the logo.png in the header in pp_newswire.  I've tried every CSS trick in the book, but the logo is still aligned left, and I can't find anything anywhere in the code that would be forcing this.

I removed the Searchbox out of the header in Administer->Site Building->Themes (both Global and pp_newswire).  There's nothing else left in the header block except for the .brand .branding block wrapper for the logo.  The logo.png is 578x99, and the .branding block defaults to .branding width-30-590 to accommodate it.

Generated HTML source shows:

<!-- HEADER -->
<div id="header" class="width-48-950 last nofloat"> <div class="branding width-30-590">
<div class="brand"><a href="/prosepoint/" title=""><img src="/prosepoint/sites/default/files/pp_newswire_logo.png" alt=""></a></div>
</div> <!-- /branding -->
</div> <!-- /header -->

I've tried adding any number of CSS formatting snippets in pp_newswire.css to make the logo align to center in the header block, all to no avail.  Some examples:

.brand {
margin: 0 auto;
width: 590px;
}

.brand {
margin-left: 186px;
}

.branding h1.brand,
.branding div.brand {
margin: 0 auto;
width: 590px;
}

.branding h1.brand a,
.branding div.brand a {
margin-left: 186px;
}

.branding .width-30-590 {
margin: 0 auto;
width: 590px;
}

.branding .width-30-590 {
margin-left: 186px;
}

None of these seems to do the trick.  So....what am I missing?  Am I simply not putting the right CSS recipe together here?  Or is there a PHP code snippet somewhere that is forcing the .brand block to the left?  Again, I'm not a programmer, but have some minor experience with CSS, and this one has me stumped.

Thank you in advance for any advice.