Border around large image display: how do I do it?

Hello,

I've been using the hybrid theme, and making css customizations to it. One thing I cannot acchieve, however, is getting a border gap (or a margin or padding) around a photo when the large version is displayed (clicking on a thumbnail gets to this point). The aim is to keep a separation of the image from the browser chrome.
Here's the bit of theme.css (with line numbers straight out of vim) I think I need to be concerned about, but because of (I think...) the fixed control buttons on the grey bar at the bottom of the view, I seem only to be able to add a gap to the top of the image.

63 div#imageview {
64     display: none;
65     position: fixed;
66     top: 0; left: 0;
67     width: 100%;
68     height: 100%;
69     z-index: 1; /* for Opera */
70     border-bottom: 1px solid transparent; /* for Firefox Mac */
71 }
72 div#imagearea {
73     overflow: hidden;
74     width: 100%; /* for IE */
75     background-color: #000; /* added by James Valentine, 19/05/2006 */
76 }
77 div#imagediv {
78     text-align: center;
79 }
80 div#imagediv img {
81     display: block;
82     margin: auto;
83     cursor: pointer;
84 }

Any help would be much appreciated.

Cheers,
J.