Even after !42821 (#254197) merged, the effective space for MR diffs on MR is still small on mobile/tablet screens. One of the main reason is too wider line number columns, which can be made more compact. ## as-is (13.9 or 13.10-pre)  cf. [the screenshot as of 13.4](/uploads/7a5b8851fb63b4ec263320dd8c34a9d9/mr-diff-before.png)) ## to-be TBU part of &331