Thanks Matvey. I found the source of the problem using Firebug. It was in the CSS being a conflict I guess with the Rockettheme template and the CSS needed by Ecwid for it to display correctly. If anyone else has this problem, I fixed it by adding this to my 'Custom CSS Themes';
/* Search Module */
.ecwid-SearchPanel-button {color: #fff;text-shadow: -1px -1px 1px rgba(0,0,0,0.75);}
.ecwid-SearchPanel-field {color: #000;text-shadow: -1px -1px 1px rgba(0,0,0,0);}
.ecwid-SearchPanel-field {border: 1px solid #474747 !important;}
.ecwid-SearchPanel-button {border: 1px solid #3F4346 !important;}
.ecwid-SearchPanel-button {background: #474747 !important;}
.ecwid-SearchPanel-button:hover {background: #5B6366 !important;}
There was only one line of CSS code for the button for the hover and the SearchPanel-field shadow text was also a problem with the template I'm using. I'm not great on CSS so it was a quick & dirty fix and no doubt it has syntax that doesn't need to be there. At least it works now.
Matvey, is there any chance someone could look at
http://www.ecwid.com/forums/showthread.php?p=56827 ? It would be good to know what to do there. Thanks for your help.