Hi,
The reason you loose the default formating is because the original TD is substituted with a new one, and this does not use the default class from SharePoint. The new TD can be styled using standard CSS so if you add this line to your custom CSS:
td.dffs-readonly,td.dffs-readonly-inner{
background-color:#FFFF66;
background-image:url();
border-top:1px silver solid;
}
You must verify the color of the border by inspecting an existing TD using the developer tools in the browser (hit F12) to match the same look.
Hope this helps,
Alexander