jquery plugin - trying to change an elements width/background

I'm using a jquery (WP) plugin to create an image slider with thumbnails underneath.
My goal is to have the main image's background be `bg.png`, with the thumbnail section background be `wood.png`.

I've changed the CSS to what I believe to be correct(see below), but the background of the thumbnail section isn't extending the full `961px`, it's restricted to the `921px` width I've established with the main image. I have a feeling this might be due to nesting within the plugin's php/jquery, I'm just not sure how to go about altering it to work. If that is the case, how do I fix it? If it's something else, how do I determine what it is/how to fix it?

Really, any and all insight, tips, advice, etc is greatly appreciated.

CSS

.thethe_image_slider.white-square-1{
    background: url('../images/bg.png');
}
.white-square-1 .thethe-image-slider-thumbnails{
    background: url('../images/wood.png');
    margin-top: 20px;
    margin-bottom: 40px;
}

Code (markup):

thethe-image-slider.php : pastebin dot com/QJD49Qhn
Live site : urbanpalate dot com/instyle-mag-ming-by-mango