I highly suggest delta[1] for viewing diffs on the command line. It pretty much replicates GitHub's diff rendering, and is quite configurable.
[1]: https://github.com/git/git/tree/master/contrib/diff-highligh...
I slightly tweaked the default config and it is great.
[core]
pager = delta
[interactive]
diffFilter = delta --color-only
[delta]
features = navigate
hunk-header-style = omit
line-numbers = true
line-numbers-left-format = "{nm:>3} "
line-numbers-right-format = "{np:>3} "
max-line-length = 0