theme css problem

Hi i use the magnificent theme in a one of my web sites
Recently i have edit and added the following custom css code to my theme

body {
background-color: #FFFFFF;
}

.titles-featured a, .titles-featured a:hover, .titles-featured, .titles a:link, .titles a:visited, .titles a:active{
font-size: 24px;
}
#content .container {
width: 1160px;
}
#sidebar-left{
float: left;
width: 300px;
}
#sidebar-right {
float: right;
width: 300px;
}
#main-content {
width: 538px;
}
.meta-info {
display: none;
}

The problem that i face now is that my theme is not centered any more
What i want to do is;
1.Centered the theme so all the posting columns look the shame.(when i try to change the values my theme broke)

2.To make the middle posting columns bigger so i can see all the posting titles…
Any idea???
My web site address is

PLEASE anyone can help i will appreciate//
Anythink you need just ask!
Thanks in advance!