The use of `m-4 text black` for the notification bell results in this
icon being shifted upwards. Instead we should use the `item` class but
adjust `not-mobile` and `mobile-only` to make their `display: none`
settings `!important`.
(As an aside: This is probably one of the only times we should use
`!important` in our less files and the rest should be avoided or
removed.)
Ref #20069
Revert #20236
Signed-off-by: Andrew Thornton <art27@cantab.net>
1e43a88578