Help Adjusting Header Image Position

I’ve been widening both my sidebar and page content using the Kubrick (default) theme. Now my header image is off-center by just a bit, but I can’t figure out how to slide it to the right so it can be centered. The page is here:

http://www.centauri-dreams.org/

My style.css file, in the Structure section, has this on the header. Help! How do I edit it to get the desired result:

#header {
padding: 0;
margin: 0 auto;
height: 200px;
width: 100%;
background-color: #73a0c5;
}

#headerimg {
margin: 0;
height: 200px;
width: 100%;
}

Can anyone tell me how to edit this to slide the header image to the right? Thanks for any help!

Paul