What version are you running?
Current 3.0 
What's the URL of the page this enhancement relates to, if any?
https://reviewboard/r/1234/diff/1#index_header
Describe the enhancement and the motivation for it.
If I click the new feature "show deleted content" of a really huge file it would be nice if I could collapse the view again like I can do with the other code snippets in the diff, e.g. "+20 -20" or the icon "=" in the middle of an expanded diff.
What operating system are you using? What browser?
Linux, Chromium and Firefox