Need CSS code to have pop-up appear Left

The Greybox pop-up, on my website, opens in the center of the page. I'm told if I want it to open on the left side of the page, I need to modify the CSS file. Can you help me add some css code so the pop-up appears on the left side of the page instead of appearing in the center of the web page?
Thanks.

Here's the code currently in the ccs file:

#GB_overlay {
    background-color: #000;
    position: left;
    margin: auto;
    top: 0;
    left: 0;
    z-index: 100;
}

#GB_window {
    left: 100;
    top: 0;
    font-size: 1px;
    position: left;
    overflow: visible;
    z-index: 150;
}

#GB_window .content {
    width: auto;
    margin: 0;
    padding: 0;
}

#GB_frame {
    border: 0;
    margin: 0;
    padding: 0;
    overflow: auto;
    white-space: nowrap;
}


.GB_Gallery {
    margin: 0 22px 0 22px;
}

.GB_Gallery .content {
    background-color: #fff;
    border: 3px solid #ddd;
}

.GB_header {
    top: 10px;
    left: 0;
    margin: 0;
    z-index: 500;
    position: absolute;
    border-bottom: 2px solid #555;
    border-top: 2px solid #555;
}

.GB_header .inner {
    background-color: #333;
    font-family: Arial, Verdana, sans-serif;
    padding: 2px 20px 2px 20px;
}

.GB_header table {
    margin: 0;
    width: 100%;
    border-collapse: collapse;
}

.GB_header .caption {
    text-align: left;
    color: #eee;
    white-space: nowrap;
    font-size: 20px;
}

.GB_header .close {
    text-align: right;
}

.GB_header .close img {
    z-index: 500;
    cursor: pointer;
}

.GB_header .middle {
    white-space: nowrap;
    text-align: center;
}


#GB_middle {
    color: #eee;
}

#GB_middle img {
    cursor: pointer;
    vertical-align: middle;
}

#GB_middle .disabled {
    cursor: default;
}

#GB_middle .left {
    padding-right: 10px;
}

#GB_middle .right {
    padding-left: 10px;
}


.GB_Window .content {
    background-color: #fff;
    border: 3px solid #ccc;
    border-top: none;
}

.GB_Window .header {
    border-bottom: 1px solid #aaa;
    border-top: 1px solid #999;
    border-left: 3px solid #ccc;
    border-right: 3px solid #ccc;
    margin: 0;

    height: 22px;
    font-size: 12px;
    padding: 3px 0;
    color: #333;
}

.GB_Window .caption {
    font-size: 12px;
    text-align: left;
    font-weight: bold;
    white-space: nowrap;
    padding-right: 20px;
}

.GB_Window .close { text-align: right; }
.GB_Window .close span { 
    font-size: 12px;
    cursor: pointer; 
}
.GB_Window .close img {
    cursor: pointer;
    padding: 0 3px 0 0;
}

.GB_Window .on { border-bottom: 1px solid #333; }
.GB_Window .click { border-bottom: 1px solid red; } 
           

Code (markup):

 

Try this..

#GB_overlay {
    background-color: #000;
    position: left;
    margin: auto 0;
    top: 0;
    left: 0;
    z-index: 100;
}

Code (markup):