How to add custom css to thumbnails

I successfully installed the plugin and the slideshow is running fine. I need to add a custom border to the active thumbnail. How can I do that?

Also, when I click on the thumbnail, I would like to display the relevant slide. Currently, the thumbnails are going to the top when I click on them.

Here is the link to the site I am working on: http://cohear.curvine.com/

Thanks,
Chandrika

https://wordpress.org/plugins/dynamic-content-gallery-plugin/