I am trying to find out a way to edit the width of the thumbnail that displays for the featured image on the "Edit Post" page (note: not the front end of the site, I'm talking about when making or editing a post and you set the featured image on Wordpress's backend). I would like it so that when I've set a featured image on Wordpress's backend, it displays to me at, say, 50px wide (and the height of course adjusts automatically).
The reason I need to do this is because I've setup my theme where I can "crop" the featured image on the front page to move up or down based on margin and padding in a custom field I've setup. That way I can "crop" the thumbnails exactly how I want. So I want the thumbnails on the Wordpress edit page to be the same height as the front end of the site so I can eyeball how much pixels to move the images up and down before posting the news story. This way, I'll be able to better center the image on the back end rather than having to publish the story then run to the front page to see how much I need to move it up or down (since the image has been sized correctly).
It would also be nice if someone could tell me how to apply a CSS class to the featured image on the backend as well. That way, I can overlay in a little ruler that can assist me in determining how much I should move the image up or down.