[Plugin: WP-Table Reloaded] Centering an image

In wp-table reloaded, I am trying to center an image horizontally in a column. I found other posts that showed some CSS for centering, but it seemed like you had to add it to the wordpress custom css, which would apply it to ALL wp-table reloaded tables, not just the one I am interested in? The only place in the “Edit table” page that looked like you could put CSS says “This is not the place to enter “Custom CSS” code!” so I’m guessing that’s not what I want ??

Any thoughts on this?

Thanks,

David