'resources/src/mediawiki.skinning/messageBoxes.css' classes are from early times in MediaWiki core, where CSS class architecture wasn't yet a thing.
The classes should be turned into
- `messagebox` => `mw-message-box`
- `errorbox` => `mw-error-box`
- `warningbox` => `mw-warning-box`
Without strong opinion if `*-box` is the right naming scheme, we're using `*-container` in a related, but slightly different context.
There would be also the possibility to use `mw-error` and `mw-error--inline` assuming that user notice boxes are the default way of exposing them.
# TODO
[x] Update includes/Html.php to add the new classes as above
[x] Update resources/src/mediawiki.skinning/messageBoxes.less to use the new classes, but retain the existing classes with a comment explaining that these are supporting on-wiki content.
[] Update the non-standard uses of success, errorbox and warningbox class to use the new methods
[] Update Vector to use the new method.
[] Write a Tech News entry (or write a draft and a desired announcement-time as a comment below)