In common word processors, it is standard to underline added text and cross-through deleted text. Changes by different people appear in different colors.
In git, conflicting changes get
<<<<<<< this is theirs ======= this is yours >>>>>>
It is plain text, so what was deleted is inferred by comparing mine vs. theirs, or by a diff per version against the common ancestor (hope I got this right)
There are some diff viewers which lock scrolling, e.g. meld diff, which means that they try to scroll two side by side versions in sync (as good as possible)