What version are you running?
Review Board 7.0
What's the URL of the page this enhancement relates to, if any?
Review page
Describe the enhancement and the motivation for it.
I fairly regularly end up reviewing code on a laptop due to open-office distractions.  Trying to see a sufficient size of diffs on a laptop screen is difficult at the best of times, but the latest RB upgrade has made this much harder by adding permanent fixed overlays at the top of the screen for the Review menu and for the names of files that are currently visible.  On my laptop these are taking up 20% of the browser real estate.  See the attached screenshot.
It is particularly irritating because over 50% of the space taken up is just blank space.  There could easily be a much more compact single line that has the Review menu on the left and just one diff link after it (I only need to see the name of one diff, the one that has its header off-screen at the top.  All the other diffs have giant header lines that are in the view anyway).  
What operating system are you using? What browser?

Please provide any additional information below.