I've never seen a stylesheet customized to that extent before! But looking through it to the extent I'm able to understand it, I think the problem has to lie in the section titled...
/* SilverFish Customizations */
...since that's the only area of the stylesheet where the body and mainwrapper locations are defined.
I'd start by laying out the element definitions in that section in separate lines so you can easily read the definitions being applied. Clarity of code helps with debugging.
so when you change this...
Code:
body {margin: 0; text-align: center; font-family: verdana, arial, helvetica, sans-serif; font-size: 62.5%; color: #00000; margin: 10px 0px 50px 0px; color: #333; background: url(../images/bg_body.gif) repeat-x #6f9db8;}
...to this...
Code:
body {
margin: 0;
text-align: center;
font-family: verdana, arial, helvetica, sans-serif;
font-size: 62.5%;
color: #00000;
margin: 10px 0px 50px 0px;
color: #333;
background: url(../images/bg_body.gif) repeat-x #6f9db8;}
... you can quickly see that you've defined margin and color twice each for the body tag. That won't be your problem, since the second definition takes precedence, but it indicates that it's going to be harder to figure out the problem than it needs to be.
You may have closed up the code that way in an attempt to save stylesheet load time. That's no longer any kind of issue. Stylesheets load in a fraction of a second.
Rob