Add custom content to jquery colorbox

I’m using jquery colorbox plugin with wordpress. I figured out how to influence the layout of cb by using css, no problems so far. But how can I add some custom content to the cb overlay e.g. a div with a logo? I already defined the css for the logo div but of course it is not showing up on overlay without implementing it in the rest of the code. But how and were? Thank you for your help.

https://www.ads-software.com/extend/plugins/jquery-colorbox/