Increase fixed layout width
The current maximum width for the fixed layout width is 1200 pixels, leaving the central part that display the differences with a width of 958 pixels. When reviewing a merge request using the side-by-side view, lines that are 120 characters long don't fit, creating two lines, making more difficult the comparison.
I propose you extend the width of the central part by around 25 pixels to make sure that they can fit 120 characters, which is a very common length limitation.